Goal:
  
  G : t
  x : V.t
  y : V.t
  z : V.t
  e : EdgeOf x y
  p : PathOf y z
  q1 : SPath (VSet.remove x (nodes p)) y x
  HG : e.π1 + sweight q1 <= 0
  IHp : weight p <= sweight (simplify2 p)
  F0 : true = true -> VSet.In x (snodes (simplify2 p))
  F1 : ~ VSet.In x (snodes (simplify2 p)) <-> true = false
  q2 : SPath (nodes p) x z
  H : sweight q1 + sweight q2 = sweight (simplify2 p)
  ============================
   (sweight q1 + e.π1 <= 0)


DEBUG:Going to execute:
intros; Zify.zify_pre_hook