diff --git a/day-13/image.go b/day-13/image.go
index aef4bf3..c19218b 100644
--- a/day-13/image.go
+++ b/day-13/image.go
@@ -16,6 +16,7 @@ func newImg() img {
 	return img{raw: make([]string, 0)}
 }
 
+// transposed rotates an image rightwards ninety degrees
 func (i img) transposed() []string {
 	transposed := []string{}