-        self.assertTrue(self.square4.__lt__(self.square3))
-        self.assertFalse(self.square3.__lt__(self.square4))
-          
-    def test_compliment(self):
-        self.assertEqual(~self.square1, self.compliment)
-    
-    def test_polyhedral_hull(self):
-        self.assertEqual(self.square1.polyhedral_hull(), self.hull)
-    
+        self.assertTrue(self.square4 < self.square3)
+        self.assertFalse(self.square3 < self.square4)
+        self.assertTrue(self.empty < self.square1)
+        self.assertTrue(self.square1 < self.universe)
+
+    def test_complement(self):
+        self.assertEqual(~self.square1, self.complement)
+        self.assertEqual(~self.universe, Empty)
+        self.assertEqual(~self.empty, self.universe)
+
+    def test_aspolyhedron(self):
+        self.assertEqual(self.square1.aspolyhedron(), self.hull)
+        self.assertEqual(self.universe.aspolyhedron(), self.universe)
+        self.assertEqual(self.empty.aspolyhedron(), self.empty)
+
+    def test_project(self):
+        self.assertEqual(self.square1.project(symbols('x')), self.dropped)
+        self.assertEqual(self.square1.project(symbols('x y')), self.universe)
+        self.assertEqual(self.universe.project([]), self.universe)
+        self.assertEqual(self.empty.project([]), Empty)
+