minor correction

Author: andrewcropper

popper/gen3.py

@@ -553,7 +553,7 @@ def find_variants3(self, rule, ruleid=0, max_rule_vars=False):
         head_arity = len(self.settings.head_literal.arguments)
         body_vars = frozenset(x for literal in body for x in literal.arguments if x >= head_arity)
         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)
         subset = range(head_arity, self.settings.max_vars)