I am interested in controlling musical textures, i.e., relations between polyphonic parts. I defined a bunch of functions that use the simple polyphonic music representation used also by my function preview-score that I presented shortly (see https://opusmodus.com/forums/topic/902-polyphonic-preview/#comment-2686). Apologies that this post is a bit longer.    Here is a particularly flexible function: map-parts transforms a polyphonic score. It is a variant of the standard Lisp function