diff --git a/day01-hard/main.scm b/day01-hard/main.scm
index 947ea07..8948cb0 100755
--- a/day01-hard/main.scm
+++ b/day01-hard/main.scm
@@ -55,7 +55,7 @@
 
 (assert-eq "flat test 1 failed"
   '(1 2 3 4 5 (6 7) 8)
-  (flat '((1 2) (3 4) (5 (6 7) 8))))
+  (flat '((1 2) () (3 4) (5 (6 7) 8))))
 
 (define (filter predicate) (reduce-right '()
   (lambda (current accumulator)
@@ -129,13 +129,10 @@
       ((compose (list
         (coalesce-not-empty (lambda () (f (cdr values))))
         flat
-        (filter id)
-        (map
-          (lambda (token)
-            ((truthy-chaining (compose (list
-              (map (prepend (car token)))
-              (lambda (rest) (f (next rest values))))))
-              (starts-with (cdr token) values))))))
+        (map (lambda (token) ((compose (list
+          (map (prepend (car token)))
+          (lambda (rest) (if rest (f (next rest values)) '()))))
+          (starts-with (cdr token) values))))))
         tokens))))))
 
 (define (tokenize tokens)