circle of fifths on umbilic torus surface
Affective Musical Key Characteristics https://wmich.edu/mus-theo/courses/keys.html
The Piano's Ivory Cage https://wmich.edu/mus-theo/groven/ivorycage.html
https://www.musikipedia.dk/dokumenter/boeger/pauer-music.pdf
Works By Difficulty https://www.pianolibrary.org/composers/bach/works-editions/