Goal:
    G : t  H : is_true false
  ============================
   (exists z : Z, None = Some z /\ z <= 0)


DEBUG:Going to execute:
<Coq.Init.Tauto.is_disj> flags X1; (solve
            [ Ltac.left; t_tauto_intuit | Ltac.right; t_tauto_intuit ])