Goal:
    _z_ : VSet.t  a : V.t
  ============================
   ((VSet.In a _z_ -> VSet.In a _z_) /\ (VSet.In a _z_ -> VSet.In a _z_))


DEBUG:Going to execute:
autorewrite with set_eq_simpl in *;
            VSetDecide.MSetDecideAuxiliary.inst_MSet_hypotheses; autorewrite
            with set_simpl set_eq_simpl in *; push not in * using
            MSet_decidability; VSetDecide.MSetDecideAuxiliary.substMSet;
            VSetDecide.MSetDecideAuxiliary.assert_decidability