def test_contains(self):
s = Sustitucion()
self.assertFalse(s.contains(Var('x')))
s.push(Var('a'), 1)
self.assertTrue(s.contains(Var('a')))
def test_contains(self):
s = Sustitucion()
self.assertFalse(s.contains(Var('x')))
s.push(Var('a'), 1)
self.assertTrue(s.contains(Var('a')))