Goal:
    z : Z  k : t  H : Some z = k
  ============================
   (None = k)


DEBUG:Going to execute:
constructor 1
Level 4: evaluation returns
<coq-core.plugins.tauto::is_unit_or_eq@0>
where
tauto_flags := 
of type
tauto_flags
X1 := None = k
of type
constr of type tacvalue