Goal:
    G1 : t  G2 : t  sub : full_subgraph G1 G2
  ============================
   (is_true
      (VSet.for_all
         (fun x : VSet.elt =>
          VSet.for_all (fun y : VSet.elt => lsp G1 x y == lsp G2 x y) (V G1))
         (V G1)))


DEBUG:Going to execute:
apply /andP ; split