Quote Originally Posted by massimobio View Post
You can use #9#5
Same voicing.
Why not allow 7#9b13?

It is not wrong. Not sure I understand the current design choice to force users to use #5.

Same for 9b13. In the latter case I would argue not only is it personal preference, but #5 is wrong. Because a chord can not have the same note twice and as there is a 5 in a 7th chord and using mixolydic with b13 9#5 would be a false description for that scale / chord. There would be a fifth in the scale and the #5 falsely suggested by the chord symbol.