Improved hints for ancestor/2 and descendant/2.

1 files changed, 7 insertions, 7 deletions

diff --git a/prolog/problems/family_relations/ancestor_2/common.py b/prolog/problems/family_relations/ancestor_2/common.py
index 9346e5f..2353eab 100644
--- a/prolog/problems/family_relations/ancestor_2/common.py
+++ b/prolog/problems/family_relations/ancestor_2/common.py
@@ -84,6 +84,13 @@ def hint(code, aux_code):
             return [{'id': 'grandparent_used_markup', 'start': m[0], 'end': m[1]} for m in marks] + \
                    [{'id': 'grandparent_used'}]
 
+        # descendant instead of ancestor (wrong direction)
+        # warning: knowledge base dependent
+        if prolog.engine.ask_truthTO(engine_id,
+            'findall(_, ancestor(william, X), L1), length(L1, 2), \
+             findall(_, ancestor(X, william), L2), length(L2, 6)'):
+            return [{'id': 'wrong_direction'}]
+
         # missing/failed base case
         if prolog.engine.ask_truthTO(engine_id,
             'findall(X/Y, parent(X, Y), L), member(X/Y, L), \+ ancestor(X, Y)'):
@@ -103,13 +110,6 @@ def hint(code, aux_code):
             else:
                 return [{'id': 'ancestor_to_oneself'}]
 
-        # descendant instead of ancestor (wrong direction)
-        # warning: knowledge base dependent
-        if prolog.engine.ask_truthTO(engine_id,
-            'findall(_, ancestor(william, X), L1), length(L1, 2), \
-             findall(_, ancestor(X, william), L2), length(L2, 6)'):
-            return [{'id': 'wrong_direction'}]
-
         # Y does not necessarily need to be a parent
         if prolog.engine.ask_one(engine_id,
             'ancestor(_, Y), \+ parent(Y, _)') == 'false':