diff --git a/README.md b/README.md
index c0bc959..a927699 100644
--- a/README.md
+++ b/README.md
@@ -30,9 +30,12 @@ Flow2DBorder.py
 
 Flow3D.py
 	Flows for 3D autonomous dynamical systems.  Options are: Lorenz, Rössler and Chua’s Circuit.
+	
+GravSynch.py
+	Synchronization of clocks in a spaceship near a black hole.  (See: https://galileo-unbound.blog/2021/05/16/locking-clocks-in-strong-gravity/)
 
 gravlens.py
-	Gravitational lensing
+	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.
@@ -65,7 +68,7 @@ NetSIRS.py
 	SIRS viral infection model on networks
 
 PenInverted.py
-	Inverted pendulum.
+	Inverted pendulum. (See: https://galileo-unbound.blog/2020/09/14/up-side-down-physics-dynamic-equilibrium-and-the-inverted-pendulum/)
 
 Perturbed.py
 	Driven undampded oscillators with a plane-wave perturbation.  Options are: pendulum and double-well potential.  These are driven nonlinear Hamiltonian systems.  When driven at small perturbation amplitude near the separatrix, chaos emerges.  These systems do not conserve energy, because there is a constant input and output of energy as the system reacts against the drive force.  Plots a two-dimensional Poincaré section.
@@ -99,7 +102,7 @@ UserFunction.py
 		linfit.py – linear regression function
 
 WebMap.py
-	The discrete map of a periodically kicked oscillator displays a web of dynamics.
+	The discrete map of a periodically kicked oscillator displays a web of dynamics.  (See: https://galileo-unbound.blog/2018/10/27/how-to-weave-a-tapestry-from-hamiltonian-chaos/)
 
 (Selected Python programs can be found at the Galileo Unbound Blog Site:
 	 https://galileo-unbound.blog/tag/python-code/)