Goal:
  
  G : t
  HI : invariants G
  HG : acyclic_no_loop G
  n : Z
  x : V.t
  y : VSet.elt
  Vy : VSet.In y (V G)
  K : Z
  G' := Subgraph1.G' G y x K : t
  Hle : Z.of_nat ((fun x : V.t => to_label (lsp G' (s G') x)) x) + n <=
        Z.of_nat ((fun x : V.t => to_label (lsp G' (s G') x)) y)
  Vx : VSet.In x (V G)
  ly : Z
  Hly : lsp G (s G) y = Some ly
  Hpos : 0 <= ly
  Hlab : Z.of_nat (to_label (lsp G (s G) y)) = ly
  lx : Z
  Hlx : lsp G (s G) x = Some lx
  poskx : 0 <= lx
  Hlab' : Z.of_nat (to_label (lsp G (s G) x)) = lx
  z : Z
  xs : lsp G x (s G) = Some z
  xy : lsp G x y = Some K
  XX : correct_labelling G (to_label ∘ lsp G' (s G'))
  HI' : invariants G'
  ============================
   (n <= K)


DEBUG:Going to execute:
<coq-core.plugins.ltac::clear@0> $1