Goal:
    z : Z  z0 : Z  z1 : Z  H : (z <= z0)%Z
  ============================
   (z1 + z <= z1 + z0)%Z


DEBUG:Going to execute:
match goal with
           | |- _ -> _ => intro; t_tauto_intuit
           | |- _ => t_reduce; t_solver
           end