From d4e24f31ab51640c2e65eb68446f0d5f6174b7e1 Mon Sep 17 00:00:00 2001
From: Aleksander Sadikov <aleksander.sadikov@fri.uni-lj.si>
Date: Wed, 2 Mar 2016 15:24:00 +0100
Subject: Improved hints for ancestor/2 and descendant/2.

---
 prolog/problems/family_relations/ancestor_2/common.py | 5 +++++
 prolog/problems/family_relations/ancestor_2/sl.py     | 8 ++++++++
 2 files changed, 13 insertions(+)

(limited to 'prolog/problems/family_relations/ancestor_2')

diff --git a/prolog/problems/family_relations/ancestor_2/common.py b/prolog/problems/family_relations/ancestor_2/common.py
index 2353eab..a7c491d 100644
--- a/prolog/problems/family_relations/ancestor_2/common.py
+++ b/prolog/problems/family_relations/ancestor_2/common.py
@@ -31,6 +31,7 @@ hint_type = {
     'descendant_need_not_be_parent': Hint('descendant_need_not_be_parent'),
     'wrong_direction': Hint('wrong_direction'),
     'only_two_levels_deep': Hint('only_two_levels_deep'),
+    'predicate_always_false': Hint('predicate_always_false'),
     'timeout': Hint('timeout'),
 }
 
@@ -84,6 +85,10 @@ def hint(code, aux_code):
             return [{'id': 'grandparent_used_markup', 'start': m[0], 'end': m[1]} for m in marks] + \
                    [{'id': 'grandparent_used'}]
 
+        # target predicate seems to always be false
+        if not prolog.engine.ask_truthTO(engine_id, 'ancestor(_, _)'):
+            return [{'id': 'predicate_always_false'}]
+
         # descendant instead of ancestor (wrong direction)
         # warning: knowledge base dependent
         if prolog.engine.ask_truthTO(engine_id,
diff --git a/prolog/problems/family_relations/ancestor_2/sl.py b/prolog/problems/family_relations/ancestor_2/sl.py
index 974bde3..de66ba4 100644
--- a/prolog/problems/family_relations/ancestor_2/sl.py
+++ b/prolog/problems/family_relations/ancestor_2/sl.py
@@ -78,6 +78,14 @@ npr. prababica ali prapradedek sta tudi prednika.</p>
 <p>Si morda sprogramiral ravno obratno in zamenjal prednika s potomcem?
 <code>X</code> naj bo prednik od <code>Y</code> in ne obratno!</p>
 <p><img src="[%@resource Prolog_ancestor_02.svg%]" /></p>
+''',
+
+    'predicate_always_false': '''\
+<p>Vse kaže, da tvoj predikat vedno vrne "false". Si mu dal pravilno ime, si se morda pri imenu zatipkal?</p>
+<p>Če je ime pravilno, se morda splača preveriti tudi, če se nisi zatipkal kje drugje,
+je morda kakšna pika namesto vejice ali obratno, morda kakšna spremenljivka z malo začetnico?</p>
+<p>Možno je seveda tudi, da so tvoji pogoji prestrogi ali celo nemogoči (kot bi bila npr. zahteva,
+da je <code>X</code> hkrati starš in sestra od <code>Y</code> ali kaj podobnega).</p>
 ''',
 
     'timeout': '''\
-- 
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