What is the target use case of the library? Aren't chord, note and interval objects redundant (i.e. a chord is a set of notes of a specific distance, where the latter is an interval)? The chords themselves are just a subset of scales, of which a finite number exists (see e.g. https://github.com/rochus-keller/musictools/). Do you consider the relation of chords and scales, and modulations within and between scales? Concerning Lisp, are you aware of https://ccrma.stanford.edu/software/s7/s7.html or https://commonmusic.sourceforge.net/?