diff --git a/21.rkt b/21.rkt
index e928b8a..3808d54 100644
--- a/21.rkt
+++ b/21.rkt
@@ -9,21 +9,20 @@
 
 (define (part1 input)
   (match-define (data lines all-is all-as tainted) input)
-  (define untainted (set-subtract all-is (apply set-union (hash-values tainted))))
-  (for*/sum ([l (in-list lines)] [i (in-set (line-is l))] #:when (set-member? untainted i))
+  (define all-tainted (apply set-union (hash-values tainted)))
+
+  (for*/sum ([l (in-list lines)] [i (in-set (line-is l))] #:unless (set-member? all-tainted i))
     1))
 
 (define (part2 input)
   (match-define (data lines all-is all-as tainted) input)
-  (define edges
-    (for*/list ([(k v*) (in-hash tainted)] [v (in-set v*)])
-      (list k v)))
-  (define G (undirected-graph edges))
+  (define G (undirected-graph
+              (for*/list ([(k v*) (in-hash tainted)] [v (in-set v*)])
+                (list k v))))
   (define matching (maximum-bipartite-matching G))
 
   (string-join
-    (for/list ([val (in-list (sort matching #{string<? (first %1) (first %2)}))])
-      (second val))
+    (map second (sort matching string<? #:key first))
     ","))
 
 ;; parse input file