diff --git a/README.md b/README.md
index 76e82de..4d6bb9f 100644
--- a/README.md
+++ b/README.md
@@ -38,7 +38,7 @@ These Python programs can be downloaded from GitHub at
 	* Gravitational lensing.  (See: https://galileo-unbound.blog/2021/04/05/the-lens-of-gravity-einsteins-rings/)
 
 * Hamilton4D.py: 
-	* Hamiltonian flows for 4D autonomous systems.  Options are: Henon-Heiles potential, and the crescent potential.  Plots a two-dimensional Poincaré section.
+	* Hamiltonian flows for 4D autonomous systems.  Options are: Henon-Heiles potential, and the crescent potential.  Plots a two-dimensional Poincaré section. (See: https://galileo-unbound.blog/2019/11/04/the-physics-of-life-the-universe-and-everything-in-one-easy-equation/)
 
 * Heiles.py: 
 	* Henon-Heiles and also a crescent model
@@ -50,7 +50,7 @@ These Python programs can be downloaded from GitHub at
 	* Hill potentials for 3-body problem.  (See: https://galileo-unbound.blog/2019/07/19/getting-armstrong-aldrin-and-collins-home-from-the-moon-apollo-11-and-the-three-body-problem/)
 
 * Kuramoto.py: 
-	* Kuramoto synchronization of phase oscillators on a complete graph.
+	* Kuramoto synchronization of phase oscillators on a complete graph. (See: https://galileo-unbound.blog/2019/11/04/the-physics-of-life-the-universe-and-everything-in-one-easy-equation/)
 
 * logistic.py: 
 	* Logistic discrete map, plus some other choices.
@@ -95,7 +95,7 @@ These Python programs can be downloaded from GitHub at
 	* The Standard Map in twist format  (See: https://galileo-unbound.blog/2019/10/14/how-number-theory-protects-you-from-the-chaos-of-the-cosmos/)
 
 * trirep.py: 
-	* Replicator dynamics in 3D simplex format.
+	* Replicator dynamics in 3D simplex format. (See: https://galileo-unbound.blog/2019/11/04/the-physics-of-life-the-universe-and-everything-in-one-easy-equation/)
 
 * UserFunction.py: 
 	* Growing library of user functions