diff --git a/day05-hard/main.scm b/day05-hard/main.scm
index 45d4af3..08a4e9b 100755
--- a/day05-hard/main.scm
+++ b/day05-hard/main.scm
@@ -101,8 +101,7 @@
 
 ;=============== concat ======================
 (define (concat left right)
-  ((reduce-right right (lambda (current accumulator) (cons current accumulator)))
-    left))
+  ((reduce-right right cons) left))
 
 (assert-eq "concat test 1 failed"
   '(1 2 3 4 5)