Goal:
    x : VSet.elt  p : VSet.t
  ============================
   (VSet.Equal (VSet.add x (VSet.add x p)) (VSet.add x p))


DEBUG:Going to execute:
repeat
            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