fix double negative

tests/utils/test_Zero.py

@@ -52,7 +52,7 @@ class Tests(unittest.TestCase):
         assert o <= -1
         assert not (o > -1)
         assert o >= -1
-        assert -(-o)*o == -o
+        assert -1.*(-o)*o == -o
         o = Identity()
         assert +o == o
         assert -o == -o