diff --git a/4/solution.nix b/4/solution.nix
index b7ed2ba..d354647 100644
--- a/4/solution.nix
+++ b/4/solution.nix
@@ -18,8 +18,7 @@ let
 
   # calc overlaps
   hasOverlap = overlapFunc: a: b:
-    let a1 = head a; b1 = head b; a2 = last a; b2 = last b;
-    in overlapFunc a1 a2 b1 b2 || overlapFunc b1 b2 a1 a2;
+    splitPair (splitPair overlapFunc a) b  || splitPair (splitPair overlapFunc b) a;
   overlaps = overlapFunc: map boolToInt (map (splitPair (hasOverlap overlapFunc)) pairs);
 in {
   part1 = sum (overlaps completeOverlap);