Goal:
  
  A : Type
  B : Type
  f : nat → A → B
  x : A
  l : list A
  IHl : ∀ n k : nat,
          k ≤ n
          → List.rev (mapi_rec f l (n - k)) =
            mapi_rec (λ (k0 : nat) (x : A), f (Nat.pred #|l| + n - k0) x)
              (List.rev l) k
  n : nat
  k : nat
  H : BinInt.Z.le (BinInt.Z.of_nat k) (BinInt.Z.of_nat n)
  cstr : BinInt.Z.le BinNums.Z0 (BinInt.Z.of_nat k)
  cstr0 : BinInt.Z.le BinNums.Z0 (BinInt.Z.of_nat n)
  cstr1 : BinInt.Z.le BinNums.Z0 (BinInt.Z.of_nat #|l|)
  ============================
   (BinInt.Z.add (BinInt.Z.of_nat #|l|)
      (BinInt.Z.max BinNums.Z0
         (BinInt.Z.sub (BinInt.Z.of_nat n) (BinInt.Z.of_nat k))) =
    BinInt.Z.max BinNums.Z0
      (BinInt.Z.sub
         (BinInt.Z.add
            (BinInt.Z.max BinNums.Z0
               (BinInt.Z.sub
                  (BinInt.Z.add (BinInt.Z.of_nat #|l|)
                     (BinNums.Zpos BinNums.xH)) (BinNums.Zpos BinNums.xH)))
            (BinInt.Z.of_nat n)) (BinInt.Z.of_nat k)))


DEBUG:Going to execute:
Zify.zify_iter_specs