commit of several large changes actually made during 2013 Dec 8-28; the following list is not exhaustive : remove superfluous type LL_Non_Empty - add Low_Level List routines {last,nonlast,catenate,slice} - add Low_Level Natural routines {plus,minus,times,divide} which are now the most fundamental math ops of the system, defined in terms of list ops - added routine LL_structure_kind - for every LL_Structure type (eg, Integer, Relation, etc), added Low_Level convenience routines both for selecting a value of that type in terms of its components and for accessing the components of a value of that type; the rest of the codebase uses these now for low-level work with structure types both for self-documentation as well as abstracting away their underlying List basis so they look like a basis of records of named fields instead - eliminated all use of a generic LL_List/Universal selector syntax ':|[...,...,*]' in favor of prior-mentioned features; it is still an open question as whether that syntax will go away entirely or not - large refactor of Low_Level {Identifier,Reference} type definitions - add routines {Low_Level.LL_same_low_level_type, Universal.same_base_type} so it is easier for the rest of the codebase to query if 2 given values belong to the same base type or not in the sense that users normally conceive of base types; for example, they would result in true if both inputs are Relation values (even if their headings differ) or both are Integer values and false if 1 Integer + 1 Relation were given (other routines will be added later that give tighter definitions of same-type, eg same relation heading, or users can make their own); the only difference between the named 2 routines so far is the first treats all Capsule as the same type and the second doesn't - removed all uses of type declaration special syntaxes {capsule_type,relation_type,tuple_type,etc} as that syntax feature is probably eliminated in favor of using more generic/flexible subset type syntax like 'Capsule where (... has_attrs ...)' instead - fixed Source_Code type to be a closed union type not an open union - added new type 'Capsule.Singleton' which consists of all Capsule types with no attributes - made large overhaul of the public Integer routine set, including fleshing out most of their definitions and adding some more (the body of 'div' is incomplete for some rounding methods) - defined the new types {Order,Less,Same,More} - defined the 10 Round_Meth types - added new file Voidlike.mdpt defining types {Voidlike,Void,Unknown,Not_Applicable} (various analogies to SQL null or Perl undef, and users can add more), and new routines '//' and 'coalesce' that work for any Voidlike type