In my opinion Bach's Art of Fugue (Kunst Der Fugue) is the greatest work of Western Classical music. It employs a variation structure like Goldberg, but tends to be more abstract. It is Bach's final work and is unfinished. I love that instrumentation is unspecified so there are many arrangements out there to listen to.

玉木さい（ウィンザー）Imagining Heaven on Earth | पुरुष tm.org 

No, but it sounds like a fascinating book

Have you read Hofstadter’s GEB? He talks extensively about it