diff --git a/README.txt b/README.txt
index 7c6c7ae..da4be03 100644
--- a/README.txt
+++ b/README.txt
@@ -4,3 +4,8 @@ dd if=/dev/zero of=./disk.img bs=1M count=1024
 losetup -fP ./disk.img
 losetup -a
 losedup -d /dev/loop0
+
+See:
+    https://github.com/landley/toybox/blob/master/toys/posix/dd.c
+    https://github.com/illiliti/libudev-zero
+    https://github.com/LoupVaillant/Monocypher