diff --git a/day20.py b/day20.py
index 6693067..9f4a192 100644
--- a/day20.py
+++ b/day20.py
@@ -81,7 +81,7 @@ def getCornerPieces(tile_dict, only_get_first_piece=False):
         for border in tile.getPossibleBorderList():
             single_borders += all_borders.count(border) - 1
 
-        if single_borders == 4:
+        if single_borders == 4:  # every border shows up twice (1x straight, 1x reversed)
             if only_get_first_piece:
                 return tile_id
             corner_pieces.append(tile_id)