Hi,

Thank you for clarifying these. I don't remember exact reason why I omit a note from 11th and 13th chords, but I think I referred some web pages to confirm these (like the following pages).

https://en.wikipedia.org/wiki/Eleventh_chord

However, since the major diatonic eleventh would create a dissonant minor ninth interval with the third of the chord, including the third is a rare phenomenon.

https://en.wikipedia.org/wiki/Thirteenth

It is customary to omit the eleventh on dominant or major thirteenth chords because the eleventh conflicts with the third

I'm not sure whether PyChord should use customary chord or not. Adding the capability for the users to modify the QUALITY_DICT can be an option.

7-13 & 7b13 means 7(b13). In my understanding, 7(b13) means b13th is appended on 7th chord (same for 7+11 & 7#11).

https://www.oolimo.com/guitarchords/G7(b13)

G7(b13) theoretically consists of the tones G (1), B (3), D (5), F (7) and Eb (b13),

I'm sure of what I'm saying. 13th chords are 7 notes chords. You cannot jump to the 13th degree without using the 11th degree. G7(b13) means G(1), B(3), D(5), F(7), A(9), C(11) and Eb(b13). That does not mean that you have to play every notes. Theorically you are on a 7 notes chord. On piano for example, G13 are often played as G(1), F(7), B(10), E(13) since these degrees are the most "significant" degrees. You just need to listen to it to understand that it sounds very interesting. Usually the other degrees are played by other instruments or are so usual so people can hear them in their mind even if you do not play them.