@Test(expected = RuntimeException.class)
 public void testNotAllowedParseLeadingIndexedVariable() {
   parser.setUpToParse("1x");
   parser.parseVariable();
 }
 @Test
 public void testParseIndexedVariable() {
   parser.setUpToParse("x1");
   Term v = parser.parseVariable();
   Assert.assertEquals(v, new Variable("x1"));
 }