diff --git a/graphics/20220725.Physics-math-illustrations.md b/graphics/20220725.Physics-math-illustrations.md
index eeeabd4..3a600e8 100644
--- a/graphics/20220725.Physics-math-illustrations.md
+++ b/graphics/20220725.Physics-math-illustrations.md
@@ -1,7 +1,7 @@
-Free Illustrations for Physics
-==============================
+Free / Open-Source Physics & Math Illustrations
+===============================================
 
-May include some that pertains chemistry, 
+(May include some that pertains chemistry, engineering and related fields.)
 
 
 
@@ -12,7 +12,15 @@ https://twitter.com/j_bertolotti/status/1030470604418428929
 
 Most of these are animated gifs.
 
-Examples:
+Here is the collection on Wikimedia:
+
+https://commons.wikimedia.org/w/index.php?search=jacopo+bertolotti&title=Special:MediaSearch&go=Go&type=image
+
+Some useful contents:
+
+* 2-D gradient descent
+  https://commons.wikimedia.org/wiki/File:Gradient_descent.gif
 
 * Moire pattern
-  https://commons.wikimedia.org/wiki/File:Moire.gif
\ No newline at end of file
+  https://commons.wikimedia.org/wiki/File:Moire.gif
+