Goal:
  
  A : Type
  B : Type
  R : nat → A → B → Type
  n : nat
  x : A
  y : B
  l : list A
  r : list B
  r0 : R n x y
  h : All2i R (S n) l r
  IHh : All2i (λ (i : nat) (x : A) (y : B), R (S n + #|l| - S i) x y) 0
          (List.rev l) (List.rev r)
  cstr : BinInt.Z.le BinNums.Z0 (BinInt.Z.of_nat n)
  cstr0 : BinInt.Z.le BinNums.Z0 (BinInt.Z.of_nat #|l|)
  ============================
   (BinInt.Z.of_nat n =
    BinInt.Z.max BinNums.Z0
      (BinInt.Z.sub
         (BinInt.Z.add (BinInt.Z.of_nat n)
            (BinInt.Z.add (BinInt.Z.of_nat #|l|) (BinNums.Zpos BinNums.xH)))
         (BinInt.Z.add (BinInt.Z.of_nat #|l|) (BinNums.Zpos BinNums.xH))))


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