A long time ago, I wrote IrisGL code for the mathematician George Francis, who made mathematical visualization his life's work. He published this book: https:/

A long time ago, I wrote IrisGL code for the mathematician George Francis, who made mathematical visualization his life's work. He published this book: https://en.wikipedia.org/wiki/A_Topological_Picturebook https://en.wikipedia.org/wiki/A_Topological_Picturebook, which is worth a look, and he was forever sketching Reimann manifolds on scraps of paper with a fountain pen. Which is quite a trick. I kick myself for not hanging onto one. He maintains what for me is a very nostalgic old-internet webpage at https://new.math.uiuc.edu https://new.math.uiuc.edu. There are links at the bottom to web versions of his computer animations. Edit: If you do click on the animations, make sure to try the different commands like "morph" and "skin".