Figures added for mother problem.

1 files changed, 11 insertions, 6 deletions

diff --git a/prolog/problems/family_relations/grandparent_2/common.py b/prolog/problems/family_relations/grandparent_2/common.py
index 98e40fc..8ccd23d 100644
--- a/prolog/problems/family_relations/grandparent_2/common.py
+++ b/prolog/problems/family_relations/grandparent_2/common.py
@@ -103,16 +103,21 @@ def hint(program, solved_problems):
             'grandparent(X, _), \+ parent(X, _)'):
             return [{'id': 'x_must_be_parent'}]
 
-        # X does not necessarily need to have a parent
-        if prolog.engine.ask_one(engine_id,
-            'grandparent(X, _), \+ parent(_, X)') == 'false':
-            return [{'id': 'x_need_not_have_parent'}]
-
         # Y must have a parent
         if prolog.engine.ask_truth(engine_id,
             'grandparent(_, Y), \+ parent(_, Y)'):
             return [{'id': 'y_must_have_parent'}]
 
+        # stop further hint testing if target predicate is always true or always false
+        if prolog.engine.ask_truth(engine_id,
+            '\+ grandparent(_, _) ; findall(X/Y, grandparent(X, Y), [A/B]), var(A), var(B)'):
+            return []
+
+        # X does not necessarily need to have a parent
+        if prolog.engine.ask_one(engine_id,
+            'grandparent(X, _), \+ parent(_, X)') == 'false':
+            return [{'id': 'x_need_not_have_parent'}]
+
         # Y does not necessarily need to be a parent
         if prolog.engine.ask_one(engine_id,
             'grandparent(_, Y), \+ parent(Y, _)') == 'false':
@@ -125,5 +130,5 @@ def hint(program, solved_problems):
         if engine_id:
             prolog.engine.destroy(engine_id)
 
-    return None
+    return []