2 files changed, 15 insertions, 4 deletions
diff --git a/prolog/problems/lists/last_elem_2/common.py b/prolog/problems/lists/last_elem_2/common.py
index 75cec75..9c44231 100644
--- a/prolog/problems/lists/last_elem_2/common.py
+++ b/prolog/problems/lists/last_elem_2/common.py
@@ -29,6 +29,7 @@ hint_type = {
     '[]_should_not_succeed': Hint('[]_should_not_succeed'),
     'list_returned': Hint('list_returned'),
     'clumsy_conc_use': Hint('clumsy_conc_use'),
+    'unsuccessful_conc_use': Hint('unsuccessful_conc_use'),
 }
 
 test_cases = [
@@ -77,15 +78,20 @@ def hint(code, aux_code):
 
         # recursion is getting bigger and bigger
 
-        # succeeds when asked to return the last element of an empty list
-        if prolog.engine.ask_truthTO(engine_id, 'last_elem([], _)'):
-            return [{'id': '[]_should_not_succeed'}]
-
         # using conc, but clumsily: conc(_, X, L) instead of conc(_, [X], L)
         if prolog.util.Token('NAME', 'conc') in tokens and \
            prolog.engine.ask_truthTO(engine_id, 'last_elem([q,a,b,c], [q,a,b,c])'):
             return [{'id': 'clumsy_conc_use'}]
 
+        # general unsuccessful use of conc, but not specifically detected
+        # return general_conc hint, not to confuse/force the student into a non-conc solution
+        if prolog.util.Token('NAME', 'conc') in tokens:
+            return [{'id': 'unsuccessful_conc_use'}]
+
+        # succeeds when asked to return the last element of an empty list
+        if prolog.engine.ask_truthTO(engine_id, 'last_elem([], _)'):
+            return [{'id': '[]_should_not_succeed'}]
+
         # returns a list, not an element as required
         if prolog.engine.ask_truthTO(engine_id, 'last_elem([q], X), is_list(X)'):
             return [{'id': 'list_returned'}]
diff --git a/prolog/problems/lists/last_elem_2/sl.py b/prolog/problems/lists/last_elem_2/sl.py
index bcc33f8..7ab8ddc 100644
--- a/prolog/problems/lists/last_elem_2/sl.py
+++ b/prolog/problems/lists/last_elem_2/sl.py
@@ -51,6 +51,11 @@ implicitno že kar v argumentih predikata (glavi stavka).</p>
 biti dolžine ena, če hočeš doseči to kar želiš. Torej vzorec oblike <code>[X]</code>, kajne?</p>
 ''',
 
+    'unsuccessful_conc_use': '''\
+<p>Uporabljaš <code>conc/3</code>? Zanimiva ideja, da se rešiti tudi tako. Vendar boš moral še malo premisliti.
+Ne pozabi, <code>conc/3</code> ima tri argumente, vsi so seznami. Premisli, kakšen vzorec potrebuješ...</p>
+''',
+
     'recursive_case': '''\
 <p>Robni primer deluje. Kaj pa rekurzivni, splošni, primer?</p>
 ''',