diff --git a/code/graph.py b/code/graph.py
index 786f63b..61098b7 100644
--- a/code/graph.py
+++ b/code/graph.py
@@ -17,7 +17,9 @@ FOOTER = """
 
 # TODO:
 # Add hidden nodes in each cluster above visible nodes connected by hidden edges and attach visible edges to them
+# - also see: https://stackoverflow.com/questions/53862417/how-to-set-head-and-tail-position-in-nodes-graphviz
 # Solve layering of clusters
+# - https://observablehq.com/@gordonsmith/church
 
 class Graph:
     def __init__(self):