Goal:
  
  G : t
  HG : acyclic_no_loop
  x : V.t
  y : V.t
  z : V.t
  e : EdgeOf x y
  p : PathOf y z
  IHp : weight p <= sweight (simplify2 p)
  F0 : false = true -> VSet.In x (snodes (simplify2 p))
  H : ~ VSet.In x (snodes (simplify2 p)) -> false = false
  H0 : false = false -> ~ VSet.In x (snodes (simplify2 p))
  ============================
   (~ VSet.In x (snodes (simplify2 p)))


DEBUG:Going to execute:
Ltac.cut X1; [ exact id | constructor 1; fail ]