Goal:
  
  z : Z
  z0 : Z
  k : t
  H : Some (Z.max z z0) = k
  H1 : (z0 <= z)%Z
  H2 : Z.max z z0 = z
  ============================
   (Some z = k \/ Some z0 = k)


DEBUG:Going to execute:
<Coq.Init.Tauto.is_empty> flags X1; elim H
Level 3: evaluation returns
<coq-core.plugins.tauto::is_empty@0>
where
tauto_flags := 
of type
tauto_flags
X1 := t
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.