Function could_be_italian_a6_resolution 

pub fn could_be_italian_a6_resolution(
    a: &[Pitch],
    b: &[Pitch],
    sixth: Option<&ItalianSixth>,
    restrict_doublings: bool,
) -> Result<bool>

Whether moving from a, an Italian augmented sixth, to b resolves it: the bass falls a semitone, the root rises one, the third falls one and the fifth moves by a third or a second. With restrict_doublings, the root may resolve only once and the third not at all.

sixth is the chord’s notes where the caller has them already, and is read off a where not.

Errors

An a that spells no Italian augmented sixth when sixth is not given.