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|)
  z1 : BinNums.Z
  H1 : BinInt.Z.lt 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)))
       ∧ z1 =
         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))
       ∨ BinInt.Z.le
           (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)))
           BinNums.Z0 ∧ z1 = BinNums.Z0
  ============================
   (BinInt.Z.of_nat n = z1)


DEBUG:Going to execute:
idtac