Goal:
  
  x : nat
  y : nat
  h : (Z.of_nat x <= Z.of_nat y)%Z
  cstr : (0 <= Z.of_nat y)%Z
  cstr0 : (0 <= Z.of_nat x)%Z
  ============================
   (Z.of_nat x + 1 <= Z.of_nat y + 1)%Z


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