Goal:
  
  A : Type
  P : nat → A → Type
  x : A
  n : nat
  tl : list A
  p : P n x
  h : Alli P (S n) tl
  IHh : ∀ (i : nat) (x : A), nth_error tl i = Some x → P (S n + i) x
  cstr : BinInt.Z.le BinNums.Z0 (BinInt.Z.of_nat n)
  ============================
   (BinInt.Z.of_nat n = BinInt.Z.add (BinInt.Z.of_nat n) BinNums.Z0)


DEBUG:Going to execute:
fun => <coq-core.plugins.zify::ITER@0>