minor correction

Author: andrewcropper

popper/gen2.py

@@ -232,7 +232,7 @@ def find_variants(self, rule, max_rule_vars=False):
         head, body = rule
         body_vars = frozenset(x for literal in body for x in literal.arguments if x >= len(head.arguments))
         if max_rule_vars:
-            subset = range(len(head.arguments), len(body_vars)+1)
+            subset = range(len(head.arguments), len(body_vars | set(head.arguments)))
         else:
             subset = range(len(head.arguments), self.settings.max_vars)
         for xs in permutations(subset, len(body_vars)):