From d9809e87882a4248e215ee423c3fdb2fb5f6ee2d Mon Sep 17 00:00:00 2001
From: Aleksander Sadikov <aleksander.sadikov@fri.uni-lj.si>
Date: Mon, 29 Feb 2016 17:40:06 +0100
Subject: Improved hints for cousin/2.

---
 prolog/problems/family_relations/cousin_2/common.py | 11 +++++------
 prolog/problems/family_relations/cousin_2/sl.py     |  1 +
 2 files changed, 6 insertions(+), 6 deletions(-)

diff --git a/prolog/problems/family_relations/cousin_2/common.py b/prolog/problems/family_relations/cousin_2/common.py
index 86ef5cc..ffebdae 100644
--- a/prolog/problems/family_relations/cousin_2/common.py
+++ b/prolog/problems/family_relations/cousin_2/common.py
@@ -97,17 +97,16 @@ def hint(code, aux_code):
             'findall(_, cousin(X, Y), L), (length(L, 14) ; length(L, 16))'):
             return [{'id': 'precedence_fail'}]
 
-        # cousin should not be brother or sister
-        # common parent, probably solved via grandparent
-        if prolog.engine.ask_truth(engine_id,
-            'cousin(X, Y), (brother(X, Y) ; sister(X, Y))'):
-            return [{'id': 'cousin_vs_sibling'}]
-
         # cousin to him/herself
         # just common grandparent is not enough
         if prolog.engine.ask_truth(engine_id, 'cousin(X, X)'):
             return [{'id': 'cousin_to_oneself'}]
 
+        # cousin should not be brother or sister
+        # common parent, probably solved via grandparent
+        if prolog.engine.ask_truth(engine_id,
+            'cousin(X, Y), parent(P, X), parent(P, Y)'):
+            return [{'id': 'cousin_vs_sibling'}]
 
         # X (or Y) does not necessarily need to be a parent
         # cousin is a symmetrical relation, so X and Y are covered by this
diff --git a/prolog/problems/family_relations/cousin_2/sl.py b/prolog/problems/family_relations/cousin_2/sl.py
index c1380bf..3719368 100644
--- a/prolog/problems/family_relations/cousin_2/sl.py
+++ b/prolog/problems/family_relations/cousin_2/sl.py
@@ -54,6 +54,7 @@ Si morda pozabil, da starša od <code>X</code> in <code>Y</code> ne smeta biti i
 <p>Kako je lahko nekdo bratranec/sestrična samemu sebi?
 Imata morda <code>X</code> in <code>Y</code> istega starša?</p>
 <p><img src="[%@resource Prolog_cousin_04.svg%]" /></p>
+<p>Poskusi prolog vprašati tole: <code>?- cousin(X, X).</code>?</p>
 ''',
 
     'cousin_need_not_be_parent': '''\
-- 
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