Hints for del/3 updated.

1 files changed, 3 insertions, 1 deletions

diff --git a/prolog/problems/lists/del_3/common.py b/prolog/problems/lists/del_3/common.py
index 65c51d1..deadbf8 100644
--- a/prolog/problems/lists/del_3/common.py
+++ b/prolog/problems/lists/del_3/common.py
@@ -97,7 +97,9 @@ def hint(code, aux_code):
             return [{'id': 'lost_heads'}]
 
         # used [X|T] instead of more general [H|T] in recursive case
-        if prolog.engine.ask_truth(engine_id, 'del(q, [a,b,c,d,q,x,y,z], [x,y,z])'):
+        if prolog.engine.ask_truth(engine_id, \
+                'findall(NL, del(q, [q,q,q,a,b,c], NL), [[q,q,a,b,c],[q,q,a,b,c],[q,q,a,b,c]]).') and \
+           not prolog.engine.ask_truth(engine_id, 'del(q, [a,b,c,q,x,y,z], [a,b,c,x,y,z])'):
             return [{'id': 'leading_heads_all_x'}]
 
         # L=[H|T] at the end of the rule; this can be detected with test cases and can be wrong (in some sense)