Goal:
  
  G : t
  l : labelling
  Gl := relabel G l : t
  HGl : correct_labelling G l
  x : V.t
  p : PathOf Gl x x
  ============================
   (weight p <= 0)


DEBUG:Going to execute:
<coq-core.plugins.ssreflect::ssrrewrite@0> $1 $2