Goal:
    x : V.t  y : V.t  p : VSet.t  a : V.t  H0 : x = a
  ============================
   (y = a \/ x = a \/ VSet.In a p)


DEBUG:Going to execute:
solve [ Ltac.left; t_tauto_intuit | Ltac.right; t_tauto_intuit ]
Level 3: evaluation returns
<coq-core.plugins.tauto::is_disj@0>
where
tauto_flags := 
of type
tauto_flags
X1 := y = a \/ x = a \/ VSet.In a p
of type
constr of type tacvalue