Goal:
    x : VSet.elt  p : VSet.t  H : ~ VSet.In x p
  ============================
   (VSet.Equal (VSet.remove x (VSet.add x p)) p)


DEBUG:Going to execute:
match goal with
           | |- context [ VSet.singleton ?t ] =>
                 VSetDecide.MSetDecideAuxiliary.abstract_term t
           | _:context [ VSet.singleton ?t ]
             |- _ => VSetDecide.MSetDecideAuxiliary.abstract_term t
           | |- context [ VSet.add ?t _ ] =>
                 VSetDecide.MSetDecideAuxiliary.abstract_term t
           | _:context [ VSet.add ?t _ ]
             |- _ => VSetDecide.MSetDecideAuxiliary.abstract_term t
           | |- context [ VSet.remove ?t _ ] =>
                 VSetDecide.MSetDecideAuxiliary.abstract_term t
           | _:context [ VSet.remove ?t _ ]
             |- _ => VSetDecide.MSetDecideAuxiliary.abstract_term t
           | |- context [ VSet.In ?t _ ] =>
                 VSetDecide.MSetDecideAuxiliary.abstract_term t
           | _:context [ VSet.In ?t _ ]
             |- _ => VSetDecide.MSetDecideAuxiliary.abstract_term t
           end