Goal:
  
  X : Type
  Y : Type
  R : nat → X → Y → Type
  n : nat
  x : X
  y : Y
  l : list X
  r : list Y
  r0 : R n x y
  a : All2i R (S n) l r
  IHa : BinInt.Z.of_nat #|l| = BinInt.Z.of_nat #|r|
  cstr : BinInt.Z.le BinNums.Z0 (BinInt.Z.of_nat #|r|)
  cstr0 : BinInt.Z.le BinNums.Z0 (BinInt.Z.of_nat #|l|)
  ============================
   (BinInt.Z.add (BinInt.Z.of_nat #|l|) (BinNums.Zpos BinNums.xH) =
    BinInt.Z.add (BinInt.Z.of_nat #|r|) (BinNums.Zpos BinNums.xH))


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