diff --git a/src/references.gmo b/src/references.gmo
index 736e831..9448724 100644
--- a/src/references.gmo
+++ b/src/references.gmo
@@ -45,6 +45,7 @@ texts by solderpunk in the {gemini} protocol
 => https://wpmedia.wolfram.com/uploads/sites/13/2018/02/15-1-1.pdf Cook, Matthew (2004). "Universality in Elementary Cellular Automata" (PDF). Complex Systems. 15: 1–40.
 => https://www.youtube.com/watch?v=xP5-iIeKXE8 A video of Conway's Game of Life, emulated in Conway's Game of Life.
 => https://aphyr.com/posts/341-hexing-the-technical-interview Hexing the technical interview
+=> https://tromp.github.io/cl/diagrams.html lambda diagrams
 
 ## studies