Goal:
    G : t  l : labelling  Gl := relabel G l : t  x : V.t  y : V.t
  ============================
   (forall p : PathOf Gl x y, weight p = Z.of_nat (l y) - Z.of_nat (l x))


DEBUG:Going to execute:
elim  =>[? /=|? ? ? [? /= /edge_map_spec2 [? [[=] ? ? ? ?]]] ? ->]