Goal:
  
  G : t
  HI : invariants G
  HG : acyclic_no_loop G
  n : Z
  x : V.t
  y : V.t
  Vy : ~ VSet.In y (V G)
  Hle : forall l : labelling,
        correct_labelling G l -> Z.of_nat (l x) + n <= Z.of_nat (l y)
  nneg : n <= 0
  n0 : x <> y
  z : Z
  H : lsp G x (s G) = Some z
  mem : VSet.In x (V G)
  G' := Subgraph1.G' G (s G) x z : t
  X : correct_labelling G (to_label ∘ lsp G' (s G'))
  HI' : invariants G'
  HG' : acyclic_no_loop G'
  e : EdgeSet.elt
  H' : EdgeSet.In e (E G)
  n1 : e..s <> y
  e0 : e..t = y
  ============================
   (Z.of_nat
      (if is_left (right n1) then 0%nat else to_label (lsp G' (s G) e..s)) +
    e..w <=
    Z.of_nat
      (if is_left (left e0) then 0%nat else to_label (lsp G' (s G) e..t)))


DEBUG:Going to execute:
apply False_rect, Vy; subst
DEBUG LTAC Evaluated term: (V.eq_dec e..t y)