diff --git a/entropy.md b/entropy.md
index aa82e4a20..0650f9858 100644
--- a/entropy.md
+++ b/entropy.md
@@ -1,4 +1,8 @@
+- a [[thing]].
+- a [[book]].
+  - [[what is entropy]]: https://math.ucr.edu/home/baez/what_is_entropy.pdf
+  - by [[john c. baez]]
 - [[entropy]] is the [[source]] of [[computation]].
 	- its destination is usually a [[state of higher order]].
 	- [[wp]] https://en.wikipedia.org/wiki/Entropy
-		- [[go]] [[wp]]
\ No newline at end of file
+		- [[go]] [[wp]]
diff --git a/what is entropy.md b/what is entropy.md
new file mode 100644
index 000000000..fcc22b5b3
--- /dev/null
+++ b/what is entropy.md	
@@ -0,0 +1,3 @@
+- a [[book]].
+  - #go https://math.ucr.edu/home/baez/what_is_entropy.pdf
+  - by [[john carlos baez]]