Function correct_rn_alteration_for_minor 

pub fn correct_rn_alteration_for_minor(
    figure: &FigureTuple,
    key: &Key,
    chord_has_major_third: bool,
) -> FigureTuple

The figure of a chord’s root corrected for a minor key, where the sixth and seventh degrees are named against the natural minor: music21’s correctRNAlterationForMinor, in its cautionary reading.

A raised sixth or seventh loses its sharp, since the lower case numeral a minor or diminished chord takes already says the degree is raised, and a natural one gains a flat as a caution. A chord with a major third keeps its sharp, because VI alone would name the chord on the lowered degree. Figures in a major key, and on any other degree, come back as they are.