diff --git a/days/day05.st b/days/day05.st
index 902a861..88fa9ce 100644
--- a/days/day05.st
+++ b/days/day05.st
@@ -1,8 +1,3 @@
-Dictionary extend [
-    at: key inA: Type [^self at: key ifAbsentPut: [Type new]]
-    at: key inA: Type add: elt [ (self at: key inA: Type) add: elt ]
-]
-
 Object subclass: Ordering [
     | beforeMap |
     initialize [beforeMap := Dictionary new]
diff --git a/days/day08.st b/days/day08.st
new file mode 100644
index 0000000..c035111
--- /dev/null
+++ b/days/day08.st
@@ -0,0 +1,38 @@
+Grid subclass: AntennaGrid [
+    | antennae |
+    rows: r [ super rows: r. self indexAntennae ]
+
+    indexAntennae
+    [ antennae := Dictionary new.
+      self allPosnsDo: [
+        :pos | | c | c := self at: pos.
+        c = $. ifFalse: [ antennae at: c inA: Set add: pos ]
+    ] ]
+
+    antinodesWithOffsets: offs
+    [ | set | set := Set new.
+      antennae do:
+          [ :posns | self putAntinodesBetween: posns into: set with: offs ].
+      ^set ]
+
+    putAntinodesBetween: posns into: set with: offs
+    [ posns do: [
+        :p1 | posns do: [
+            :p2 | p1 = p2 ifFalse: [
+                self antinodeFrom: p1 to: p2 into: set with: offs.
+                self antinodeFrom: p2 to: p1 into: set with: offs.
+            ]]]]
+
+    antinodeFrom: src to: dst into: set with: offs
+    [ | delta pos | delta := dst - src.
+      offs do: [
+          :off | pos := dst + (delta * off).
+          (self isInBounds: pos) ifFalse: [^self].
+          set add: pos ]]
+]
+
+AOC input: [ AntennaGrid new rows: stdin toLines asArray ];
+    part1: #(1);
+    part2: (0 to: 9999);
+    result: [ :grid :part | (grid antinodesWithOffsets: part) size ];
+    finish.
diff --git a/days/utils.st b/days/utils.st
index 8112623..df8fd3a 100644
--- a/days/utils.st
+++ b/days/utils.st
@@ -255,6 +255,11 @@ Object subclass: Grid [
     printOn: st [ rows do: [ :r | st << r; nl ] ]
 ]
 
+Dictionary extend [
+    at: key inA: Type [^self at: key ifAbsentPut: [Type new]]
+    at: key inA: Type add: elt [ (self at: key inA: Type) add: elt ]
+]
+
 Integer extend [
     ceilingDiv: denom [ ^((self - 1) // denom) + 1 ]