Abstract:
An educational toy that lets the user experiment with assembling components of different shapes in a variety of ways. The toy introduces new methods and means for assembling building blocks allowing the user to assemble them to one configuration and then to change over to other configurations by rotating, pivoting, rolling, or shifting one or more of the already assembled building blocks. The toy can introduce the user to number systems and arithmetic and geometric principles.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to an educational toy that lets the user experiment with assembling components of different shapes in many different ways. The toy of the present invention introduces new methods and means for assembling building blocks. It allows to assemble building blocks to one configuration and then to change over to another configuration or shape by rotating, pivoting, rolling, or shifting one or more of the already assembled building blocks. 
     There are existent several toys incorporating flexible semirigid articulation of solid shapes in series. The following have concepts or capabilities related to the present invention: 
     U.S. Pat. No. 1,201,710 (FINCH): a toy set with a large diversity of different shaped grooved blocks held in fixed positions against each other by elastic bands to form figures. 
     U.S. Pat. No. 3,222,072 (DREYER): a manipulative puzzle. It is a set of 27 cubic blocks fixed in sequence on an elastic cord. The preferred figure or arrangement of the blocks is a cube. 
     U.S. Pat. No. 3,597,872 (YENNOLA): a manipulative toy of 16 cylindrical blocks fixed in sequence on an elastic cord. The blocks can be rotated relative to each other to form different figures. 
     U.S. Pat. No. 4,466,799 (ARGIRO): an instructional manipulative device for multiplication computation. It is a set of 81 sequentially numbered blocks forming a number line which may be folded between any block. It is designed for use on a flat surface. 
     U.S. Pat. No. 3,514,893 (PAKSY): a manipulative toy in which a flat series of polygons linked by spring mechanisms allows to form new formations by rolling and shifting adjacent polygons. 
     U.S. Pat. No. 4,484,406 (MATSUMOTO): a manipulative toy and puzzle using 24 triangular prism blocks fixed in sequence with mechanisms between adjacent blocks which allow to rotate blocks relative to adjacent blocks. 
     U.S. Pat. No. 2,825,178 (HAWKINS): A manipulative toy with a variable number of rectangular blocks fixed in sequence on an elastic cord. 
     U.S. Pat. No. 3,577,673 (MONESTIER): a manipulative toy with a variable number of cubic blocks in fixed sequence arranged on an elastic cord. 
     U.S. Pat. No. 4,997,375 (HEINZ): an open ended manipulative and educational device with symmetrical polyhedron blocks threaded on an elastic cord. 
     Educational Objectives and Advantages 
     One of the preferred objectives of the present invention is to provide a flexible educational resource, a manipulative which can serve a number of educational and developmental processes. More specifically: to provide an open-ended educational/developmental manipulative for mathematical concept learning, eye hand (perceptual-motor) development, systematic thinking, creative play as well as open-ended construction and entertainment with transformable spatial designs. 
     The users learn, teach or simply relax by assembling unique sets which they use to create and transform numeric patterns, geometric and aesthetic spatial designs, or symbolic figures. Affective involvement opens up further possibilities for broader social/language, creativity and language development. 
     Most prior art spatial design toys have a predetermined set of elements and as a result, a predetermined set of possible configurations. The present invention provides the means for the users to create their own transformable formations. They are free to use a unique set of blocks organized according to their own particular purpose. 
     While conserving the ordinary attribute or building block that is, the individual pieces can be stacked or laid out to form designs or constructions upon flat surfaces), the pieces can also be organized and threaded (much as one would thread beads) on an elastic strand. Then, as tension is applied, the blocks are held together along the length of the strand, and it becomes a semi-plastic medium for exploring a great variety of transformable two and three dimensional configurations according to the interests of the user. 
     While the open-ended possibilites are fundamental, this does not exclude its use for closed ended activities. It is expected that adults will often determine that some particular concept (or other learning need) will be served by a certain set or arrangement of blocks. To this end, they will prearrange sets of blocks and direct a sequence of activites appropriate for the particular needs of the learners. 
     The following are some of the important areas of learning for which the present invention may serve as an improvement resource: Manual dexterity, various aspects of language and thought development (colors, spatial relationships, sequence, planning, predicting, etc.), mathematics (counting, conservation of value, base 10 and other base systems, addition and subtraction, multiplication and division, two and three dimensional geometric principles, volume, cubic number, etc.). 
     Along with all the above, the affective dimension is very important. Children tend to see symbolic figures in any of the shapes and designs that can be created by this device. This not only stimulates their imagination and creative capacity but often is what integrates the more acedemic kind of learning into their personalities and intelligence. FIGS. 1 through 4 have been included to show in a minimal way the educational applications of this device. 
     Obviously, elements of this invention can be applied to fixed assembly transformable figures. Some things that come to mind: transformable logos, signs or messages that can be changed, doll joints, novelty toys, worry beads, etc. 
     Certainly puzzles can be created, with certain configurations as the solution. Table games could be developed where the moves are step by step changes in the interfaces, moving toward a configuration which achieves a goal. 
     Combined with non-elastic cord, rope or cable, and a means for taking up and letting out slack (tightening and loosening tension), this invention could have applications in diverse kinds of strong temporary, semi permanent, or even permanent constructions (toy or otherwise). 
     A form of this invention might be used as a highly adjustable arm, such as on a robot or for a lamp (to precisely position and direct the light). 
     The interlocking patterns on identical interfaces and the identical half shells for side threading could have applications in stacking containers or other items which need to be precisely aligned, or for snaps, and any other opposing element that normally are either female or male. 
     DESCRIPTION OF THE INVENTION 
     The present invention is an open ended manipulative and educational device. It achieves a much broader range of capabilities than all the prior art. The objectives of the present invention are: 
     Simple and generalized principles for keeping the threading cord on a common central axis. 
     Achieve stability between adjacent building blocks, as well as in the total assembly of building blocks. 
     Maintain and improve the ease of threading and cord binding. 
     Provide more ways of threading and more ways to combine sets of building blocks, add flexibility and efficiency. 
     Keep cord ends hidden, yet accessible, thus adding aesthetic appeal and facilitating the more adequate formation of certain configurations. 
     The use of identical matching elements on interlocking pieces avoids the distraction of having to discern which elements correctly match each other. 
     Improve perceptibility of the structures and mechanisms which encourages active thinking and understanding while successfully manipulating the device. 
     The most significant and overriding innovation in the present invention is the use of the hollow shell. The hollow shell offers several advantages for the use and functioning of this educational device. It enables the user to understand the simple principles of maintaining common central axis orientation: 
     a) The surface slot and endings afford the essential structure, not as deep a slot as in prior art. 
     b) For longer slots that traverse an entire side, a centering guide is necessary. The center guide may be located on the opposing surface or in the center of the block. 
     Specific Features of the Invention 
     1: Identify and clarify principles for keeping the threading cord on central axis. This allows manufacturers to produce new type of building blocks according to requests from educators. 
     The hollow shell helps to highlight these principles. 
     2: Stability of the configuration prevents individual building blocks from slipping and rotating relative to an adjacent building block. Stability is achieved by use of light weight hollow shell and building blocks with interlocking features. 
     3: The features `flexibility` and `ease of use` relate to: 
     a) ease of threading by use of smaller end sections at the end of the elastic cord and the width of the slots for threading the cord in the building blocks; 
     b) ease of cord binding by providing multiple choices for terminating an elastic cord in or at a terminating building block using a cross piece terminator or a binding narrow slot of a building block; 
     c) hiding cord ends; and 
     d) combination of multi threading and cord termination. 
     Cord ends are hidden by terminating the end of an elastic cord inside the building block and where it does not interfere with other adjacent building blocks of a configuration of building blocks. Narrow binding slots inside certain building blocks and cords with notched ends provide for this feature. Cross piece terminators can be used with building blocks having no narrow slot facility. 
     A suitably formed cord end allows to thread the cord through holes containing already another cord. Side threading allows combination of independent assemblies of building into one new configuration of building blocks. Terminating cross pieces and narrow slots allow to terminate more than one cord in the same building block. 
     The side threading feature allows to insert a side threading building block into an existing assembly of building blocks without disassembly. 
     Multiple component building blocks consist of identical elements with identical interlock mechanisms to avoid confusion and distraction with which part is to fit into which other part. 
     4: Easy perceptibility of structure and mechanisms. Active thinking and understanding is encouraged during manipulation of the device because of hollow shells, transparent material, open sided building blocks, limited multiple slots in the same plane, and side threading. 
     The educational toy of the present invention includes a number of different building blocks which can be threaded on elastic cords to form two or three dimensional configurations. As soon as tension is applied to the elastic cord, the building blocks are held together in a selected configuration. The building blocks are polyhedrons of several different types. Each of the different types of building blocks has a distinct shape and means for interfacing with the elastic cord and for interfacing with adjacent building blocks. Building blocks are selected according to the configurations the user wants to implement and according to the desired interface of adjacent building blocks. 
     The building blocks are hollow bodies made from light weight material to keep the total weight of an assembly of blocks on an elastic cord as low as possible. It has been found, that with the weight of the individual building block assembled on a cord, the tension necessary to maintain a desired configuration has to be increased to prevent individual building blocks from changing their positional relationship with an adjacent building block. The building blocks of the present invention incorporate a number of features which improve maintainability of a desired configuration of building blocks. 
     The Description of the Preferred Embodiment includes descriptions of various major building blocks, building block assemblies, building block interfaces, the cords used to assemble building blocks to configurations, and methods and means for terminating the threading cords. The way and manner of assembling and modifying building block configurations is discussed with the various types of building blocks. 
     In the description of the building blocks the following definitions are used: While the expression polyhedron relates to solids bounded entirely by planes, in the context of this description hollow bodies with opposing open sides (called cookie cutters) are also included in the term polyhedron. The polygons that bound a polyhedron are called faces; the segments in which two faces come together are called edges; the end-points of edges are called vertices; the angle between two half-planes that meet at an edge is the face-angle between the two faces. 
     In principle all building blocks of the present invention have slots for guiding the elastic cord which is threaded through the building blocks. In some of the building blocks the arrangement of slots determines the common axis of adjacent building blocks. Other building blocks include separate means to establish a common axis of adjacent building blocks. 
     The following definitions relate to the description of the building blocks and the assembly of multiple building blocks and the transformation of the interface of adjacent building blocks. 
     
         ______________________________________Configuration        two or three dimensional transformable        assembly of building blocks.Transform    to change a configuration of building        blocks without disassembling.Central common axis        axis connecting the centers of two        adjacent building blocks.Polyhedron shell        a three dimensional building block having        at least three circumferential planes.Slot         An elongated opening in the surface of a        building block extending over at least two        adjacent faces.roll         changing the relative position of adjacent        building blocks by rolling a building        blocks around a common edge with an        adjacent building block so that the two        building blocks interface with their        respective faces on the other side of the        edge.pivot        changing the relative position of adjacent        building blocks by rotating a building        block around an axis perpendicular to the        common axis with an adjacent building        block for changing the interfacing face        of the rotated building block.shift        changing the relative position of adjacent        building blocks by moving one building        block in such a manner that the        orientation of the building block is not        changed but the interfacing faces of two        adjacent building blocks are changed.rotate       changing the relative position of adjacent        building blocks by rotating one building        block around the common axis with the        adjacent building block but maintaining        the same interfacing faces.Side threading        1) a method of adding a building block to        existing configuration of        threaded building blocks by expanding the        threading cord and sliding a building        block with its slot over the exposed        threading cord;        2) method of assembly in which first base        components of multi-component building        blocks are placed side-by side, the elastic        cord is routed along the sequence of        building blocks stretched and secured,        and finally the remaining components of        the building blocks are united with the        base components.Cord binding a method of terminating the elastic cord at        a building block.Side intertion        A method for linking two assemblies of        building block, where the cord of one        assembly is stretched between two        building blocks to receive a building        block of the second assembly; the building        block of the second assembly has to have        a suitable slot into which the stretched        cord of the first assembly can be slid.______________________________________ 
    
    
    
     SHORT DESCRIPTION OF THE FIGURES 
     FIG. 1 is an illustration of an assembly of building blocks forming a snake, a two-dimensional single thread configuration. 
     FIG. 2 is an illustration of an assembly of building blocks forming a base and an attached arm like a crane. 
     FIG. 3 is an illustration of an assembly of building blocks forming an athlete in spread leg position, a multiple thread, two-dimensional configuration. 
     FIG. 4 is an illustration of an arrangement of building blocks using the same assembly as used in the arrangement of FIG. 3, forming the three-dimensional figure of an ice or roller skater. 
     FIGS. 5a and 5b are illustrations of assemblies using a cubic building block to demonstrate the threading of the elastic cord for straight configuration and different corner configurations of building blocks. 
     FIG. 6 is an illustration of an assembly using an 8 faced polyhedral ring building block to demonstrate the threading of the elastic cord for straight, 45 degree angle and 90 degree corner configurations. 
     FIG. 7 is an illustration of an assembly using a cubic building block for demonstrating rotational, rolling, shifting, and pivotal movement of adjacent building blocks. 
     FIG. 8 is an illustration of a two-part cubic building block demonstrating the side threading insertion of an additiona; building block into an existing assembly of threaded building blocks. 
     FIGS. 9a through 9c are illustrations of the elastic cord and termination tools used to string the building blocks of the present invention. 
     FIG. 10 is a perspective view of a cookie cutter type cubic building block. 
     FIG. 11 is a perspective view of a first type wedge building block. 
     FIG. 12 is a perspective view of a second wedge type building block which has closed triangular faces and an open-sided interface. 
     FIG. 13 is an illustration of a tetrahedron with two double slots. 
     FIG. 14 is an illustration of a hexagonal cookie cutter building block. 
     FIG. 15 is an illustration of a cubic building block (hexahedron) having two slots crossing each other on one face. 
     FIG. 16 is an illustration of a cubic building block having two slots each extending over three faces. 
     FIG. 17 is an illustration of the octagonal polyhedral ring building block having a pair of planar 180° slots with one of two attachments for transforming the body into a 16-face polyhedron. 
     FIG. 18 is an illustration of a building block having two 90° offset pairs of planar 180° slots with one to four attachments for transforming the building block into a 16-face polyhedron. 
     FIG. 19 is an illustration of a disassembled two part cubic building block designed to be inserted into an existing configuration of building blocks. 
     FIG. 20 is an illustration of a disassembled two part hexagonal building block designed to be inserted into an existing configuration of building blocks. 
     FIG. 21 is an illustration of a disassembled two part octagonal ring building block. 
     FIGS. 22a and 22b are illustrations of a building block with a 360 degree slot, a central common axis guide and a rotational polyhedron body. 
     FIG. 23 is an illustration of two cubic building blocks with enforced edges which prevent rotation and slipping of adjacent blocks. 
     FIG. 24 is an illustration of another interlocking pattern for building blocks. 
     FIG. 25 is an illustration of an interface for preventing rotational and sliding movement between adjacent building blocks. 
     FIG. 26 is an illustration of a building block interface as described with reference to FIG. 25. 
     FIG. 27 is an illustration of the components of a building block having two slots each extending over three faces assembled from 4 equal bodies. 
     FIG. 28 is an illustration of a hexagonal ring building block as shown in FIG. 14 but having two additional slits for side threading. 
     FIG. 29 is an illustration of a disassembled cubic building block with two two-face slots in a common plane FIGS. 30a, 30b and 30c are illustrations of building blocks assembled from two boxlike halves. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIGS. 1 through 4 are illustrations of assemblies using cube shaped building blocks with edges shaved off at 45 degrees. The building blocks are in a row and then transformed by rolling, rotating, pivoting or shifting adjacent building blocks to form the shown configuration. 
     FIG. 1 is an illustration of an assembly of building blocks forming a snake, a two-dimensional single thread configuration. All building blocks are threaded on one elastic cord. Adjacent building blocks interface at their flat surfaces. The configuration is the result of a transformation by rolling and shifting selected building blocks. 
     The snake of FIG. 1 is assembled from 27 polyhedrons each having 18 surfaces, 6 major surfaces and 12 minor surfaces at 45 degree angle between the major surfaces. Two building blocks which may be used for such a configuration are disclosed in more detail with reference to FIGS. 17 and 18. The 27 polyhedron building blocks are strung on one elastic cord. After stretching the cord the ends of the cord are secured in the first building block 8 and last building block 9. The `snake` is formed by rolling selected building blocks of the stringed building blocks relative to the adjacent building blocks. Head 1 of the snake is formed by two parallel rows 10 and 11 of three building blocks. 
     The body of the snake consists of five segments 2 through 6 of 3 building blocks each, and a tail segment 7 of two times three building blocks. Segment 2 angles off head 1 at 135 degree by clockwise rotation of segment 2 from segment 11. Segment 3 angles off segment 2 135 degree by counter-clockwise rotation of segment 3 from segment 2. Segment 4 angles off segment 3 at 90 degree by clockwise rotation of segment 4 from segment 3. Segment 5 angles off segment 4 at 45 degree by counter-clockwise rotation of segment 5 from segment 4. Segment 6 angles off segment 5 at 90 degree by clockwise rotation of segment 6 from segment 5. Tail segment 7 angles off segment 6 at 90 degree by counter-clockwise rotation of segment 7 from segment 6. (All rotations seen from the top.) 
     FIG. 2 is an illustration of an assembly of building blocks forming a base and an attached arm like a `crane`. This configuration uses the same type and number of building blocks as the `snake` of FIG. 1. The `crane` is the result of a transformation by shifting, rolling, or rotating selected building blocks. 
     Base 21 of the `crane` in FIG. 2 consists of 6 segments of 3 building blocks each. Bottom layer 22 has three segments just placed next to each other in one plane, that means the first and second segment angle off at 180 degree in one direction and the second and third segment angle off each other at 180 degree in the opposite direction. The first building block of the fourth segment angles off the last building block of the third segment at 90 degree upwards, the second building block of the fourth segment angle at 90 degree of the preceding block and establishes the direction of the fourth segment. The fifth and sixth segments run parallel to the fourth segment in a plane parallel to the plane of bottom layer 22. The fourth, fifth and sixth segment constitute top layer 23 of base 21. 
     Arm 24 of the `crane` begins at the last block of the sixth segment, the rear corner of base 21. It is not a straight arm and consists of three segments 25, 26, and 27 each consisting of three building blocks. While each segment of the `crane` in FIG. 2 consists of three building blocks, it is not a requirement of the system, however, the two configurations of FIGS. 1 and 2 demonstrate how one assembly can be transformed into two different configurations. 
     The configurations shown in FIGS. 1 and 2 are first assembled by threading the required number of building blocks on an elastic cord, and then after tension is established it can be transformed to the desired configuration by rolling, rotating, or shifting selected building blocks relative to their adjacent building blocks. 
     FIGS. 1 and 2 also illustrate how to use this invention to develop an understanding of multiplication, division, volume and cubic numbers. 
     FIGS. 1 and 2 are illustrations of different configurations of the same assembly. In the straight configuration the assembly can be thought of as a number line from 1 to 27. Section 8a is made up of 10 light colored blocks, section 8b, contains another 10 blocks colored in a contrasting darker color, while section 8c contains 7 white blocks. 
     Children who have become thoroughly familiar with counting, base 10 concepts, and addition and subtraction soon discover to quickly if not instantly recognize the number of any particular block on the number line. They do this by seeing its position relative to, and within, the groups of 10. 
     As well, they know that the number line attributes hold constant even as the line is folded and doubled back on itself. 
     FIG. 1 illustrates how folding by segments of 3 will provide a kinesthetic model, not only of counting by three, but any number from 1 to 9, times 3. Likewise it will show any number between 3 and 27, divided by 3. 
     FIG. 2 illustrates how, after folding the number line at every segment of three blocks, folding back again by three forms square layers of 9 (3×3) blocks and ultimately a cube (expressed 3×3×3 or 3 2 ) whose volume is 27 blocks. 
     FIG. 3 is an illustration of an assembly of building blocks forming an athlete with spread legs, a multiple thread assembly, two-dimensional configuration. 
     The configuration shown in FIG. 3 consists of three assemblies of threaded building blocks. A first assembly 31 includes a large building block 32 in place of the head of the athlete and 5 small building blocks 39a through 39e for the rump. A second assembly 33 consists of 2 segments 34 and 35 of each 4 blocks. The third assembly 36 consists of two segments 37 and 38 of 6 blocks each. 
     To combine the three assemblied 31, 32, and 33 for the athlete of FIG. 3 assembly 33 is split between segments 34 and 35. The exposed elastic cord is inserted into the third block 39b of assembly 31 establishing the arms of the athlete. Assembly 36 is split between segments 37 and 38, and the exposed elastic cord is inserted in the last block 39e of assembly 31 establishing the spread legs of the athlete. 
     In general, a second string of building blocks can be attached to a first string of building blocks in three different ways: 
     1) by threading the cord of the second string of building blocks through the building block of the first string before the second string of building blocks is fully assembled; 
     2) by stretching the cord of the second string between two selected building blocks and squeezing the exposed stretched cord in between two building blocks of the first string of building blocks; 
     3) if the first string of building blocks has at the location of intersection with the second string of building blocks a building block with a slot across the interfacing surface with an adjacent building block and slot extensions on interface surfaces with building blocks of the second string of building blocks, then the exposed stretched cord of the second string of building blocks can be slid into that slot of the selected building block of the first string of building blocks. The ends of the slots used have to establish one common central axis with the adjacent building blocks of the inserted string of building blocks. 
     FIG. 4 is an illustration of the same assembly used the arrangement shown in FIG. 3, however, some of the building blocks have been repositioned relative to their adjacent blocks, resulting in a new configuration, a three-dimensional figure of an ice or roller skater. 
     FIGS. 5a, 5b, and 6 through 8 are illustrations of different ways to route the elastic cord through building blocks to achieve different postures of adjacent building blocks. These Figures help understanding the different ways to transform a configuration by changing the relative position between adjacent building blocks using four different operations. 
     FIG. 5a is an illustration of a straight configuration of cubic building blocks 50a through 50i and termination of elastic cord 51 at the ends of the assembly. For demonstration purposes all building blocks have been oriented in the same direction. FIG. 5b shows routing of elastic cord 51 through the building blocks after the configuration shown in FIG. 5a is transformed by rotating and pivoting selected building blocks or segments of building blocks. 
     The assembly of FIG. 5a consists of 9 transparent and hollow blocks 50a through 50i, an elastic cord 51 and two terminators 52a and 52b. The function of terminators 52a and 52b are described in more detail with reference to FIG. 9. Blocks 50a  through 50i are open sided hollow cubic bodies as shown in detail on FIG. 10. Each of the building blocks 50a through 50i have two slots crossing opposing edges (see FIG. 10). Each of the two slots has two slot sections which end at the center of adjacent faces. To form the shown configuration of building blocks 50a through 50i cord 51 is threaded through the slots of the building blocks and finally tension is established and the cord is secured in the terminal building blocks. In FIG. 5a one end of cord 51 is held in place by terminator 52a on the inside of the lower slot of building block 50a. Cord 51 is threaded through the upper slot and lower slot of building block 50b and upper slot of block 50c and so forth until it is threaded through building block 50i. As soon as tension is established on cord 51 a clamping terminator 52b is placed on cord 51. 
     To transform to the configuration of FIG. 5a to the configuration shown in FIG. 5b the first two blocks 50a, and 50b remain in their relative position. 
     Step 1: Building block 50c together with blocks 50d through 50i is rotated counterclockwise (seen from the top of the assembly) relative to building block 50b so that its front side points to the right. 
     Step 2: Stacked blocks 50d through 50i are shifted to the right and upwards relative to blocks 50a through 50c and then rotated by 180 degree so that block 50d interfaces with a side face of block 50c. 
     Step 3: To start on the next corner arrangement block 50e, together with blocks 50f through 50i, is pivoted clockwise (seen from the front). Now blocks 50f through 50i point downwards. 
     Step 4: To start the last corner so that blocks 50h and 50i point towards the viewer in FIG. 5 block 50g, together with blocks 50h and 50i, is rotated counterclockwise. 
     Step 5: The last steps for establishing the configuration of FIG. 5b are to pivot block 50h together with block 50i from the bottom face of block 50g to the front face of block 50g, and to rotate building block 50i counterclockwise. 
     FIG. 5b clearly shows how the ends of the slots at corners of a configuration establish the common axes for adjacent building blocks; and how elastic cord 51 is routed between centers of faces of adjacent building blocks. 
     As can be seen in FIG. 5 the configuration can easily be changed by stretching cord 51 between blocks 50d and 50e, and then rotating the configuration consisting of blocks 50e through 50i counterclockwise. The result would be a configuration having a straight center section consisting of blocks 50d through 50f. 
     FIG. 6 is an illustration of an partial assembly using an 8 faced polyhedral ring building block to demonstrate the threading of the elastic cord for straight, 45 degree, and 90 degree corner assemblies. The 8-faced polyhedral ring building block used in this assembly for demonstration is described in detail with reference to FIG. 17. 
     The 8-faced polyhedral ring building blocks 69a through 69d used in the configuration shown in FIG. 6 are of the cookie-cutter type. They consist of two octagonal rings 60a and 60b held spaced apart and in a co-axial arrangement by a board 60c, see building block 69c. The spacing between octagonal rings 60a and 60b provides for a pair of planar 180° degree slots around the entire circumference. In terms of functioning this pair of slots consist of two opposing slots overlapping in the same plane. Board 60c has a hole 61 in the center and two slots 62a and 62b on either side of hole 61 and spaced from hole 61. Hole 61 establishes the common axis with adjacent building blocks. Slots 62a and 62b extend to the ends of board 60c into the space between octagonal rings 60a and 60b to allow interfacing with another building block on surfaces connected with board 60c. The configuration of FIG. 6 demonstrates the routing of elastic cord 68 for a straight center-center interface between blocks 69b and 69c, a 90 degree interface between blocks 69a and 69b, and a 45 degree interface with a 90 degree rotation from block 69c to 69d. 
     FIG. 7 is an illustration of an assembly using cubic building block for demonstrating rotational, shift, roll, and pivotal movement of adjacent building blocks. The configuration uses four blocks 70a, 70b, 70c and 70d. Cord 71 passes through blocks 70a, 70b, 70c and 70d in a similar fashion as cord 51 passes through blocks 50c, 50d, and 50e. In FIG. 7 arrows are used to indicate the freedom of movement between adjacent blocks. 
     Rolling is a rotational movement of a building block around the common edge with an adjacent building block: Building block 70a is rolling around common edge 77 it shares with building block 70b as indicated by arrow 77b. It is changing its relative position from being placed on top of building block 70b to being attached to the left side of building block 70b. Both the building blocks 70a and 70b change interfacing surfaces. 
     Shifting a building block is demonstrated at the interface of building blocks 70b and 70c. (In this description it is disregarded that building block 70a is attached to building block 70b.) As indicated by arrow 74b building block 70b is first moved to the left until it can be moved downwards to a position where it attaches to the left side of building block 70c. In this operation the basic orientation of building block 70b is not changed. However, both the building blocks 70b and 70c change interfacing surfaces. At the end of this movement cord 71 passes through the slot section in the left side of building block 70b and the slot section in the right side of building block 70c. Common axis is established by these two slot sections. 
     Rotate (arrow 76a) and pivot (arrow 76b) operations are demonstrated with reference to building block 70d. In a pivot operation only the pivotted building block changes the interfacing surface. In a rotate operation no interface surface between adjacent building blocks is change, however, the rotated building block changes the orientation of all surfaces not normal to the common axis with the adjacent building block. 
     FIG. 8 illustrates how two-part cubic building blocks can be inserted into an existing assembly of threaded building blocks. In FIG. 8 a linear chain of blocks represented by blocks 80a and 80b is being expanded by insertion of two blocks 81 and 82. Blocks 80a and 80b are cubic bodies with two slots. For expansion box type cubic bodies 81 and 82 are used. Blocks 81 and 82 each have a base section 81a, 82a and a top section of which only top section 81b of building block 81 is shown in FIG. 8. After stretching cord 84 base sections 81a and 82a are inserted. Placing the top sections over the corresponding base sections completes the insertion. Blocks 81 and 82 can be shifted, rotated and pivoted in the same fashion as the equivalent single part block shown in FIG. 7. 
     FIG. 9 is an illustration of the elastic cord and termination tools used to assemble configurations of building blocks of the present invention. Except where building blocks include special slots for terminating a cord (see FIGS. 17, 18, and 21) separate terminators are required at the first and last building blocks of a configuration. 
     FIG. 9a is an illustration of a cord 90 having a round main section 90a with a first diameter, a tail section 90b with a smaller diameter and a conic front section 90c. The tip of front section 90c is inserted into the center hole 91a of terminator 91. By pulling on the tip of front section 90c it is stretched and thinned so that terminator 90 can be moved towards center section 90a. After releasing the pull on cord 90 terminator 91 is safely anchored on cord 90 (see FIG. 9b). When stretching cord 90 the diameter of the cord in center section 90a is reduced, however, the form of the cord beyond terminator 91 is maintained. In a similar manner cord end sections 90b and cord center section 90a can be stretched so that terminator 91b can be moved toward center section 90a. 
     Portion 91c of terminator 91 is squared oto a width nearly that of the slots in the polyhedron shells. When the crosspiece portion 91d is perpendicular to the slot, squared portion 91d slips into the slot and prevents the terminator from inadvertently slipping out of its holding position. 
     Another method of termination is shown in FIG. 9b at the right end of cord 90. Terminator 92 has the form of a cloth pin and is slipped over a part of center section 90a of cord 90. When cord 90 is stretched between terminators 91 and 92 the terminal part of center section 90a of cord 90 maintains its diameter and secures terminator 92. 
     The functionality of the cord can be improved by using a shaped cord such as cord 95 in FIG. 9c. Cord 95 has thin front and tail sections 95a and 95b to ease threading of terminators and building blocks. The diameter of cord 95 increases from the diameter of the front and tail sections 95a and 95b to the diameter of center section of cord 95 in sections 95c and 95d, which are of short length. Close to the ends of center section 95e there are two circumferential grooves 95f and 95g which can be used to secure cord 95 in special narrow slots provided with some of the building blocks, as will be described with reference to FIG. 17. 
     Description of the Building Blocks 
     FIG. 10 is a perspective view of a cookie cutter type cubic building block. The cubic block is formed like a cookie cutter with four equal sized square faces 101a, 101b, 101c, and 101d. The remaining two sides of the cube are open. Each one of the four faces 101a through 101d includes a slot 102a, 102b, 102c, and 102d. Slots start about a quarter of the slot width beyond the center of a face and are arranged in pairs. The first slot consists of slot sections 102a and 102b meeting at common edge 103a of faces 101a and 101b, and the second slot consists of slot sections 102c and 102d meeting at common edge 103b of faces 101c and 101d. An elastic cord routed through slot section 102a can hold an adjacent body on faces 101a. An elastic cord routed through slot section 102b can hold an adjacent body on faces 101b. An elastic cord routed through slot section 102c can hold an adjacent body on faces 101c. An elastic cord routed through slot section 102d can hold an adjacent body on faces 101d. Routing an elastic cord through slot section 102a and 102c placed the building block of FIG. 10 in a one sequence with two other building blocks. Routing an elastic cord through slot section 102b and 102d placed the building block in a different sequence with two other building blocks. Routing an elastic cord through slot section 102a and 102d placed the building block of FIG. 10 as a corner piece between two other building blocks. In that case the elastic cord is routed at 45 degree between slot sections 102a and 102d. Routing an elastic cord between slot sections 102b and 102c provides for another corner formation with two other building blocks. 
     As can be seen the slots provide for an easy way to change from a linear arrangement of three building blocks, using a building block of FIG. 10 as a center building block, to a corner arrangement, using this building block as a corner piece. 
     FIG. 11 is a perspective view of a first type wedge building block. The wedge body is established like a cookie cutter by three equal sized square faces 111a, 111a, and 111c. The two remaining triangular faces of the wedge building block are open. The two faces 111a and 111b include each a slot section 112a, respectively 112b. The slot sections start about a quarter width of the slot beyond the center of a face and are arranged the so that they meet at the common edge of faces 111a and 111b. Face 111c has a hole 113 in the center. An elastic cord threaded through hole 113 can hold an adjacent body on either one of faces 111a and 111b. The building block of FIG. 11 provide for a 60 degree corner in a configuration of building blocks. 
     FIG. 12 is a second wedge type building block which has closed triangular faces 122a and 122b and three square faces 122c, 122d and 122e, of which bottom face 122e is open. Bottom face 122e has four borders 123a through 123d. Borders 123a through 123d extend over less than half the length of the edges of bottom face 122e. When interfacing the second wedge type body with its open-sided bottom face 122e with an equally sized interface surface of another building block borders 123a through 123d prevent this second wedge type building block from sliding off the common central axis of the adjacent body. 
     The two faces 122c and 122d include each a slot 124a, 124b, respectively. The slots start at the center of a face and are arranged so that they meet at the intersection of faces 122c and 124d. An elastic cord threaded through either slot 124a or slot 122b is to be centered by the adjacent building block on which face 122e rests. 
     FIG. 13 is an illustration of a tetrahedron with two double slots. In FIG. 13 the tetrahedron has three faces 131a, 131b, and 131c and a bottom face 131d. Slot sections 132a and 132b in faces 131a and 131b start about one quarter of the width of the slot beyond the center of their respective face and meet in the middle of the common edge of the two faces. Slot sections 132c and 132d in faces 131c and 131d start about one quarter of the width of the slot beyond the center of their respective face and meet in the middle of the common edge of the two faces. 
     FIG. 14 is an illustration of hexagonal ring building block seen from its bottom side and having six faces 141a, 141b, 141c, 141d, 141e, and 141f. The bottom side and top side are open, so this building block belongs to the group of cookie cutters. Faces 141a, 141b, and 141c share slot 142a. Faces 141d, 141e, and 141f share slot 142b. Slot 142a starts about a quarter of the width of the slot beyond the center of face 141a, traverses face 141b, and ends about a quarter of the width of the slot beyond the center of face 141c. Slot 142b starts about one quarter of the width of the slot beyond the center of face 141d, traverses face 141e, and ends about one quarter of the width of the slot beyond the center of face 141f. Two separators 143a and 143b are attached at the inside of the body where faces 141a and 141f, respectively where faces 141c and 141d meet. Separators 143a and 143b leave a gap running perpendicular to slots 142a and 142b. The gap between separators 143a and 143b in combination with slots 142a and 142b centers a cord threaded through the two slots and the gap. 
     The hexagonal ring building block is used to interface other building blocks in a straight line, 60 degree or 120 degree angles. 
     FIG. 28 is an illustration of a hexagonal ring building block as shown in FIG. 14, however, this hexagonal ring building block is made from elastic material and includes slits 280a and 280b in faces 281a and 281b respectively. Slits 280a and 280b provide for side threading, i.e. slits 280a and 208b can be opened by bending opposite quarter surfaces 281a and 281b, respectively 282a and 282b, which enables the user to insert the building block of FIG. 28 into an existing assembly of building blocks without disassembly. 
     FIG. 15 is an illustration of another cube (hexahedron) having two slots 151a and 151b crossing on topside 152a and extending to the centers of faces 152b, 152c, 152d, and 152e. Face 152f has a hole 153 in the center for centering the threading cord. 
     FIG. 16 is still another cubic building block having two slots 161a and 161b. Slots 161a and 161b each span three faces of the cubic block. The planes of slots 161a and 161b are perpendicular to each other. When a threaded cord enters and exists from contiguous faces of the hollow body the cord is routed directly at a 45° angle through the interior between the opposing slots. When modifying interfacing with this block more attention (and often more steps) is necessary to orient the direction of the slots correctly for the desired change. 
     FIG. 17 is an illustration of a octagonal polyhedral building block 171 with one of two attachments 172 for converting the body into an (16)-side polyhedron. The attachments 172 do not have a slot and provide no functionality for stringing building blocks. 
     The 8-sided polyhedral cookie cutter type building blocks 171 consists of two octagonal rings 171a and 171b held spaced apart and in a co-axial arrangement by a board 171c. The spacing between octagonal rings 171a and 171b provides for a pair of planar 180° slots. Board 171c has a hole 176 in the center for establishing a common axis between adjacent building blocks. Two slots 175a and 175b on either side of hole 171c and spaced from hole 176 extend to the ends of board 60c into the space between octagonal rings 171a and 171b. Slots 175a and 175b provide for proper interfacing with other building blocks when the elastic cord of the assembly has to extend in the direction of board 171c. 
     The octagonal ring building block 171 includes narrow extension slots 173a and 173b of slots 175a and 175b in board 171c. Narrow extension slots 173a and 173b can be used to terminate a threading cord having a termination groove as shown in FIG. 9d. Such a termination is shown in FIG. 6 in a building block 60d. Board 171c could incorporate a hook for side threading. This could be done by replacing hole 176 and slot 173b with a hook such as hook 222a in FIG. 22a. The octagonal ring building block 171 can be modified by attaching on one or both open sides an attachment 172 thereby forming a closed polyhedron building block. Because attachment 172 does not have any slots it cannot interface with any other building block. 
     A two piece octagonal polyhedral building block which could be disassembled across slots for side threading (unlike block 210 of FIG. 21, which divides along the slot) would be similar and slip together like sections 300a and 300b of FIG. 30a or section 305 in FIG. 30b. Board 171c would be incorporated in one of the sections or better divided at hole 176 and incorporated into each half. 
     FIG. 18 is an illustration of a octagonal building block 180 with two 360 degree slots 181a and 181b. Building block 180 consists of four corner sections 182a, 182b, 182c, and 182d interconnected with each other by board 182e. Board 182e has a threading hole 183 in the center and four slots 184a, 184b, 184c, and 184d extending into the spaces between sections 182a through 182d. Slots 184a through 184d connect to narrow extension slots 185a through 185d. Narrow extension slots 185a through 185d are provided for terminating an elastic cord of the type shown in FIG. 9d. 
     While building block 180 is shown in FIG. 18 as a functional building block, there are different ways to manufacture it, first it can be glued or welded together from five pieces 182a through 182d and board 182e, or it could be assembled from two sections, each including two corner pieces and half of a board 182e. Both sections may include additional means for assembling and disassembling the functional building block in a fashion similar to those of the building block of FIG. 21. In that case building block 180 would allow side threading, insertion in an existing assembly of building blocks. 
     Building block 180 can be complemented by corner insert 186 to close the open corners. 
     FIG. 19 is an illustration of a two part building block 190 designed to be inserted into an existing configuration of building blocks without disassembly of the configuration. Building block 190 consisting of base 190a and top 190b has the same characteristics as the cubic building block shown in FIG. 10, expect that it can be inserted into an existing configuration as described with reference to FIG. 8. 
     FIG. 20 is an illustration of a two part hexagonal building block 200 designed to be inserted into an existing configuration of building blocks. It consists of two equal hexagonal sections 201a and 201b each having extensions for establishing two slots between the sections and to link the two sections. Separators 204a and 204b provide for an internal slot in section 201a, separators 204c and 204d provide for an internal slot in section 201b. Functionally building block 200 corresponds to building block 140 described with reference to FIG. 14. Each of the sections 201a and 201b has two outer links 202a and 202b, and two inner links 202c, and 202d which determine the length and width of the slot between sections 201a and 201b. Outer links 202a and 202b overlap with inner links 202c and 202d, respectively when both sections are put together to form one building block 200. Separators 204a through 204d have links 203a through 203d. Link 203a overlaps with link 203c, link 203b overlaps with link 203d when sections 201a and 201b are put together. Separators may include grooves or notches to provide for a positive closure when assembling the two sections to a building block. 
     FIG. 21 is an illustration of a disassembled two part octagonal ring building block 210. Both sections 211a and 211b of building block 210 are identical. Section 211a consists of an octagonal ring 212a, and separator 213a connecting the centers of two opposite sides of octagonal ring 212a. Connected to separator 213a are two linking tongues 213b and 213c spaced apart by a slot width. Tongues 213b and 213c are offset from the center of separator 213a. Separator 213a includes two recesses 213d and 213e just next to tongues 213b and 213c and offset from the center of separator 213a by the same space as tongues 213b and 213c for receiving a corresponding tongue of the second section 211b of building block 210. 
     When assembling a building block 210 from sections 211a and 211b tongues 213b and 213c of one section extend into recesses 213d and 213e of the other section to provide for a 360 degree slot between the octagonal rings 212 of the two sections 211a and 211b. Tongues 213b and 213c each include a narrow slot 215a and 215b for terminating an elastic cord as shown in FIG. 6. 
     FIGS. 22a and 22b are illustrations of a building block with a 360 degree slot, a central common axis guide and a rotational polyhedron body. The body consist of two equal shells 220a and 220b mounted on a central body 220c spaced apart to provide a 360 degree slot 225a for receiving a cord 221 used to assemble this body 220 and other bodies to a configuration of building blocks. Cord 221 is held in a hook 222a which serves as common axis guide. Cord 221 is either threaded through the opening of hook 222a or cord 221 is inserted sideways into slot 225a, sufficiently stretched to reduce the diameter, and then squeezed under downward pressure through gap 222b into hook 222a. 
     The two shells 220a and 220b are each rotatably mounted on central body 220c. In FIG. 22a the body shells 220a and 220b consist of a octagonal ring 224a and a frustrum 224b of an 8-sided pyramid. The top surface of fustrum 224b includes the means for rotatably connecting shell 220a to central body 220c. When interfacing a building block as shown in FIG. 22 with other building blocks in an assembly shells 220a and 220b will assume rotational positions in which the surfaces of octagonal rings 224a are aligned. There is no restriction in using other shell bodies in place of those shown in FIG. 22 as long as they include equally sized polyhedron rings. 
     Central body 220c includes two short tongues spaced apart to provide a narrow slot 225b. Narrow slot 225b is aligned with slot 225a of the building block. Slot 225b can be used to terminate cord 221 in a fashion as shown in FIG. 6. 
     Central body 220c carries at both ends cylindrical bearings 226a and 226b with grooves 227a and 227b. Shells 220a and 220b have corresponding bearing means consisting of a cylindrical opening in the top of fustrum 224a. FIG. 22b is a view of center body 220c and shell 220a. Inside the cylindrical opening there is a rind 228a protruding into the open space. During assembly of the body this ring 228a is slid into groove 227a of bearing 226a. Shell 220b is rotatably mounted on center body 220c in the same fashion as shell 220a. 
     Description of Different Block Interfaces 
     FIGS. 23 through 26 are illustrations of building block interfaces which ensure that adjacent blocks remain in a desired position to each other. 
     FIG. 23 is an illustration of a cubic building blocks 230 with reinforced edges which prevent rotation and slipping of adjacent blocks. Building block 230 has the same slot arrangement as building block 100 in FIG. 10, two slots with each 2 slot sections, crossing two opposite edges. In FIG. 23 only one slot 231 is visible. All 8 edges of surfaces parallel to slot 231 of building block 230 have each one indented edge section and one protruding section like indented section 232 and protruding section 233 of edge 234 of block 230. All four edges perpendicular to the plane of the slots are indented to receive protruding sections when the interface is rotated by 90°. When blocks with enforced edges are placed in an adjacent positions protruding sections fit into indented sections. Once tension is established in the cord which is threaded through the building blocks, the blocks tend to remain in the configuration established by the user. 
     FIG. 24 is an illustration of a different interlocking pattern for building blocks. Instead of subdividing an edge into two sections each edge consists of many small protruding zones 240 spaced apart by suitably sized recesses 241 to receive protruding zones of an adjacent building block. The protruding zones and recesses could as well be arranged in circles of different radii around the center of an interface surface. 
     FIG. 25 is an illustration of a building block interface for preventing rotational and shift movement between adjacent building blocks. The fan type interface consists of an arrangement of substantially triangular planes 250 arranged with a small alternating positive and negative angle to common plane 251 of an interface surface of a building block. Triangular planes 250 extend in radial direction from center 252 in plane 251. Such an arrangement included in the interfacing faces of two adjacent blocks prevents unintentional rotation and shift between the two blocks. In FIG. 25 the fan type interface includes a hole 253 through which the elastic cord can be threaded for assembly with other building blocks. A fan type interface could be combined with a slot end or with a slot passing through the interface surface. 
     FIG. 26 is an illustration of a building block interface as described with reference to FIG. 25. In FIG. 26 the interface of FIG. 25 is applied to faces smaller than the diameter of the interface. Furthermore, the two interfacing faces 260a and 260b of two building blocks include slots 261a and 261b. Slots 261a and 261b are just opening in the interface pattern and do not interfere with the function of the same. 
     If there are the same number of pairs of negative and positive angled planes per section, such as a quadrant section, on an interface surface then interfacing surfaces will be aligned at rotational distances of the size of the sections. 
     FIG. 27 is an illustration of the four components 270a, 270b, 270c, and 270d of building block which has two three-sided slots when fully assembled. The two three-sided slots are in planes normal to each other. Body 270a is one corner piece of a cubic building block which when fully assembled is similar to the one shown in FIG. 16. The building block of FIG. 27 results from a horizontal cut through the middle of the building block of FIG. 16. The plane of such a cut is normal to the two planes of the two three-sided slots and goes through the four center points of the ends 273a, 273b, 273c, and 273d of the two three-sided slots. 
     All four components of this building block are equal, therefore only component 270a will be described in detail. Component 270a includes one long side 271b, and two short sides 271a and 271c which are one side of the rims of a three-sided slot. The other long side 272 includes a semicircular recess 273a which is one of the terminal ends of the other three-sided slots of the assembled building block. Long side 272 includes two recesses 274a and 274b symmetrically spaced from recess 273a to receive locking tongues of adjacent corner pieces. 
     The two short sides 271a and 271c carry locking tongues 276a and 276b to interlock with recesses 277a and 277b of adjacent corner pieces 270c, respectively 270d. 
     FIG. 29 is an illustration of a disassembled cubic building block with two two-sided slots in a common plane, similar to the building block described with reference to FIG. 19. The two halves of the building block result from a cut in the plane perpendicular to the plane common to the two slots 291a and 291b. In FIG. 29 upper body 292a includes the inner rim 293a and lower body 292b includes the outer rim 293b which allows to assemble building block 290 like a box. Of course there are other ways of keeping block 290 assembled, such as suitably placed tongues and recesses as disclosed with reference to FIG. 27. 
     FIG. 30a is an illustration of another cubic building block which can be disassembled for side threading. The building block of FIG. 30a consists of an outer section 300a and an inner section 300b. Inner section 300b is sufficiently smaller than outer section 300a to just fit inside outer section 300a. Section 300a has an open ended single surface slot 301a and an open ended dual surface slot 301b. Section 300b has an open ended single surface slot 302a and an open ended dual surface slot 302b. Both inner section 300b and outer section 300a can be used as independent building blocks and offer side threading capability by the open ended slots. Inner section 300b can be inserted into outer section 300a as indicated in FIG. 30a, resulting in a closed building block equivalent to the building block of FIG. 10. However, if one of the two sections is rotated 180 degree so that the open ended single surface slots match and the open ended dual surface slots match then the assembled building block is similar to that of FIG. 15 having a round opening in one surface opposite to a three surface slot. 
     For easier handling open slot end 303a and slot 303b of outer section 300a can be widened to ease holding inner section 300b when disassembling this type of building block. In FIG. 30a open slot end 303a and slot 303b are widened by suitable sized quarter circular sections 309a, 309b, 309c, and 309d, respectively. Other cut-out forms may be used to suit other applications. 
     FIG. 30b is an illustration of one section of a cubic building block which provides for side threading. The building block of FIG. 30b consists of two equal sized sections 305 which can be put together to make up a closed building block equivalent to the building block of FIG. 10. Section 305 consists of an outer half section 306a and an inner half section 306b. Outer and inner half sections are sized so that inner half section of one section 305 fits into the outer half section 306b of another section 305. In FIG. 30b slot 307a traverses front face 308a of outer half section 306a and meets slot end 307b of bottom face 308b; front face 308c of inner half section 306b includes slot end 307c. Other slot arrangements including slots in the side faces of the two half sections are possible. FIG. 30c is an illustration of a building block assembled from two building block sections of the type shown in FIG. 30b. 
     FIG. 31 is an illustration of an octangonal building block which can be disassembled for side threading. The building block of FIG. 31 consists of two portions 310a and 310b which fit together at overlapping circumferential sections 311a and 311b to form a building block similar to block 171 with cap portion 172 of FIG. 17. Section 311a slips over section 311b to a position where edge 314a joins edge 314b and boarder 315b buts against straight element 315a. Slots 312a and 312b of section 311b receive board 313a to a position where there remains a space between boards 313a and 313b forming a centering guide opening for a cord threaded through the building block. 
     As indicated in the description of the various building blocks, there are a number of features shared by several of the building blocks. All of the building blocks are polyhedrons. Flat surfaces are the basic feature to provide a stable interface with an adjacent Building block. Furthermore, the stability of the interface with an adjacent building block is provided by the common axis principle of the design. Slots are used to provide the possibility to change the interfacing surfaces, thereby changing the configuration of an assembly withyout having to disassemble an assembly of building blocks on a core. Four different ways to move adjacent building blocks relarive to each other and the combination of the same are used to change configurations. TABLE 1 correlates the various features of the educational toy of the present invention with the FIGS. 1 through 31. 
     
                       TABLE 1______________________________________Building Block ClassificationsCHARACTERISTIC         FIGURES______________________________________a)  Polyhedron shell    one piece building block    cookie cutter type, open sided                      10, 11, 14, 28                      17, 18, 20, 21    contiguous surfaces    10, 11, 12, 13, 14,                      15, 16, 19, 20    divided surfaces       17, 18, 21, 22    symmetrical in 3 dimensions                      13, 15, 16, 18, 19    two piece building block    cut along slots        19, 20, 21, 31    cut across slots       29, 30    four piece building block                      27    cut across slotsb)  Common axis determined by    slot    slot endings in faces only                      10, 11, 12, 13, 19                      29, 30    slot endings in faces or                      15, 16, 27    opening in opposite face    slot endings in faces or                      14, 20, 28    internal guide    internal guide only    17, 18, 21, 22, 31    hole in face           11, 15    adjacent block, surface interlock                      12c)  Slot arrangement    Slot length    two face slots         10, 11, 12, 13, 19,                      29, 30    &gt;2 face slots          14, 15, 16, 20, 31                      17, 18, 21    360 degree slot        22    Slot relation    single                 10, 13, 14, 16, 19,                      20, 27    pairs of 180° slots, overlapping                      17, 18, 21, 31    intersecting ensemble  15, 18    opposing in common plane                      10, 14, 17, 19, 20,                      21, 22, 28, 29, 30,                      31    opposing in different planes                      13, 16, 27    opposing in common and different                      18    planesd)  relative movement between adjacent    building blocks    rotation               2, 4, 5, 6, 7    pivoting               4, 5, 7    shifting               1, 2, 4, 5, 6, 7    rolling                1, 2, 4, 6, 7e)  locks for preventing unintended    movements between adjacent building    blocks    edge implementation    12, 23, 24    face implementation    25, 26    circular type on face  24f)  cord termination (cord binding)    cross piece, clothes pin                      9    narrow slot            6, 17, 18, 21, 31g)  assembly    single cord assembly   1, 2    multiple cords linked assembly                      3, 4h)  threading methods    serial threading       5, 6, 7, 10, 11, 12,                      13, 14, 15, 16, 17, 18    side threading    divides building block 8, 19, 20, 21, 27, 29,                      30, 31    slit                   28    hook                   22    open insertion         15, 16, 17, 18, 21, 31    along single central axis slot______________________________________ 
    
     While a great number of different building blocks have been described in detail, the above tabular presentation of the features included in the described building block shows that still other building blocks can be designed using different combinations of the listed features without departing from the basics of this invention.