Goal:
  
  A : Type
  B : Type
  R : nat → A → B → Type
  l2 : list A
  r2 : list B
  n : nat
  h2 : All2i R (n + 0) l2 r2
  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:
zify_saturate