theorem
  GS is [Graph-like] iff _GraphSelectors c= dom GS & the_Vertices_of GS
is non empty & the_Source_of GS is Function of the_Edges_of GS,the_Vertices_of
GS & the_Target_of GS is Function of the_Edges_of GS,the_Vertices_of GS by Lm1;
