diff --git a/4/solution.nix b/4/solution.nix
index 225a0a0..341aa90 100644
--- a/4/solution.nix
+++ b/4/solution.nix
@@ -4,20 +4,26 @@ let
   # read input
   input = readFile ./input;
   pairs = let 
-    readRange = s: let
-        l = splitString "-" s;
+    readRange = s:
+      let l = splitString "-" s;
       in [ (toInt (head l)) (toInt (last l)) ];
     readPair = a: b: [ (readRange a) (readRange b) ];
-  in map (line: split readPair (splitString "," line)) (splitString "\n" input);
+  in map
+    (line: split readPair (splitString "," line))
+    (splitString "\n" input);
 
-  partiallyContainsOther = a1: a2: b1: b2:
+  # overlap functions
+  partialOverlap = a1: a2: b1: b2:
     a1 <= b1 && b1 <= a2 || a1 <= b2 && b2 <= a2;
-  containsOther = a1: a2: b1: b2: a1 <= b1 && a2 >= b2;
-  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;
+  completeOverlap = a1: a2: b1: b2:
+    a1 <= b1 && a2 >= b2;
+
+  # 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;
   overlaps = overlapFunc: map boolToInt (map (split (hasOverlap overlapFunc)) pairs);
 in {
-  part1 = sum (overlaps containsOther);
-  part2 = sum (overlaps partiallyContainsOther);
+  part1 = sum (overlaps completeOverlap);
+  part2 = sum (overlaps partialOverlap);
 }
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