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


DEBUG:Going to execute:
<Coq.Init.Tauto.is_empty> flags X1; elim H
Level 3: evaluation returns
<coq-core.plugins.tauto::is_unit_or_eq@0>
where
tauto_flags := 
of type
tauto_flags
X1 := exists z0 : Z, Some z = Some z0 /\ z0 <= 0
of type
constr of type tacvalue

Level 3: Backtrace:

Tactic failure.
Level 3: Backtrace:

Tactic failure.
Level 2: Backtrace:

Tactic failure.
Level 2: Backtrace:

Tactic failure.