  We construct embeddings G of the category of graphs into categories of
R-modules over a commutative ring R which are almost full in the sense that the
maps induced by the functoriality of G
  R[Hom_Graphs(X,Y)] --> Hom_R(GX,GY) are isomorphisms. The symbol R[S] above
denotes the free R-module with the basis S. This implies that, for any
cotorsion-free ring R, the categories of R-modules are not less complicated
than the category of graphs. A similar embedding of graphs into the category of
vector spaces with four distinguished subspaces (over any field, e.g. F_2={0,1}
is obtained).
