Hint for conc/3 corrected.

1 files changed, 4 insertions, 4 deletions

diff --git a/prolog/problems/lists/conc_3/common.py b/prolog/problems/lists/conc_3/common.py
index 58152a6..108a334 100644
--- a/prolog/problems/lists/conc_3/common.py
+++ b/prolog/problems/lists/conc_3/common.py
@@ -82,6 +82,10 @@ def hint(code, aux_code):
         # recursion is getting bigger and bigger
 
 
+        # base case succeeds with arbitrary result
+        if prolog.engine.ask_truthTO(engine_id, 'conc([], [a,b,c], L), var(L)'):
+            return [{'id': 'base_case_arbitrary'}]
+
         # shortening the second list instead of first list
         if prolog.engine.ask_truthTO(engine_id,
            'conc([a,b,c], [1,2,3,4], L), (L = [1,2,3,4,a,b,c] ; L = [4,3,2,1,a,b,c])'):
@@ -108,10 +112,6 @@ def hint(code, aux_code):
                 return [{'id': 'two_heads_markup', 'start': m[0], 'end': m[1]} for m in marks] + \
                        [{'id': 'two_heads'}]
 
-        # base case succeeds with arbitrary result
-        if prolog.engine.ask_truthTO(engine_id, 'conc([], [a,b,c], L), var(L)'):
-            return [{'id': 'base_case_arbitrary'}]
-
         # missing/failed base case
         if not prolog.engine.ask_one(engine_id, 'conc([], [qa,qb,qc], [qa,qb,qc])'):
             return [{'id': 'base_case'}]