2 files changed, 27 insertions, 1 deletions
diff --git a/prolog/problems/family_relations/sister_2/common.py b/prolog/problems/family_relations/sister_2/common.py
index 2c9528e..9be9e6d 100644
--- a/prolog/problems/family_relations/sister_2/common.py
+++ b/prolog/problems/family_relations/sister_2/common.py
@@ -45,3 +45,8 @@ def test(program):
             prolog.engine.destroy(engine_id)
 
     return n_correct, len(queries)
+
+def hint(program):
+    if '\=' not in program and '\==' not in program:
+        return [{'id': 'x_y_must_be_different'}]
+    return None
diff --git a/prolog/problems/family_relations/sister_2/en.py b/prolog/problems/family_relations/sister_2/en.py
index d8395c0..629123c 100644
--- a/prolog/problems/family_relations/sister_2/en.py
+++ b/prolog/problems/family_relations/sister_2/en.py
@@ -11,4 +11,25 @@ description = '''\
     X = patricia.
 </pre>'''
 
-hint = {}
+hint = {
+    'x_y_must_be_different': '''\
+<p>What if <code>X</code> and <code>Y</code> are the same person? Try the
+following query:</p>
+<pre>
+?- sister(sally, Y).
+</pre>
+''',
+
+    # TODO move to generic prolog/en.py
+    'no_hint': '''\
+<p>No hint available, sorry! Try to use thinking instead.</p>
+''',
+
+    # TODO move to generic prolog/en.py
+    'syntax_error': '''\
+<p>Your code contains syntactic mistakes. The Prolog compiler emitted the following messages:</p>
+<pre>
+[%=messages%]
+</pre>
+''',
+}