Title: Naturaleza del grafo
Description: This book leaves from the equation characteristic of Euler for geometry.
 The author proposes an extension for this equation adding the number of crossings between the edges. It makes a review on the complete, bipartite and circular graphs. It proposes a theorem for the arcs of a graph, the segments of edges.
 It raises what is a occupied graph, something that I see for the first time. It raises a fundamental equation for flat polygons, where it distinguishes between edge and side. The edges are those that we can see, the sides are abstract, thus being born new polygons that can be classified. The author calls segmentales figures to them. It offers some exercises solved on it. 
The equation of Carder is a generalization of the Euler equations and the extension that the author for no connected graphs proposes. Peculiar note is a problem that solves where a drawing and by means of only three constants obtained from he himself can be made, another person would be able to represent he himself drawing.
Subjects: Graph theory