Goal:
  
  G1 : t
  G2 : t
  sub : subgraph G1 G2
  acG2 : acyclic_no_loop G2
  x : V.t
  p : PathOf G1 x x
  ============================
   (weight p <= weight (map_path (subgraph_on_edge sub) p))


DEBUG:Going to execute:
apply : Z.ge_le ; apply : weight_map_path2  => ? ? [? ?] /=