Goal:
    s : VSet.t  x : VSet.elt  H : VSet.In x s  y : VSet.elt  H0 : VSet.In y s
  ============================
   (x = y \/ VSet.In y s)


DEBUG:Going to execute:
solve [ Ltac.left; t_tauto_intuit | Ltac.right; t_tauto_intuit ]
Level 2: evaluation returns
<coq-core.plugins.tauto::is_disj@0>
where
tauto_flags := 
of type
tauto_flags
X1 := x = y \/ VSet.In y s
of type
constr of type tacvalue