Goal:
    G : t  z : Z  H : is_true (z <=? 0)
  ============================
   (exists z0 : Z, Some z = Some z0 /\ z0 <= 0)


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