Goal:
  
  G : t
  HI : invariants G
  HG : acyclic_no_loop G
  n : Z
  x : V.t
  y : V.t
  Vy : VSet.mem y (V G) = false
  e : n <= 0
  l : labelling
  Hl : correct_labelling G l
  k : Z
  Hk : lsp G x (s G) = Some k
  Hxs : n <= k
  p : SPath G (V G) x (s G)
  Hp : sweight p = k
  H : Z.of_nat (l x) + weight (to_pathOf G p) <= Z.of_nat (l (s G))
  ============================
   (Z.of_nat (l x) + n <= Z.of_nat (l y))


DEBUG:Going to execute:
<coq-core.plugins.ssreflect::ssrrewrite@0> $1 $2
DEBUG LTAC Evaluated term: Hk
DEBUG LTAC Evaluated term: Hk
DEBUG LTAC Evaluated term: (lsp0_spec_eq G k Hk)
DEBUG LTAC Evaluated term: (correct_labelling_PathOf G l Hl x 
                              (s G) (to_pathOf G p))