Function local_key 

pub fn local_key(
    degree: &str,
    global_key: &str,
    from_dcml: bool,
) -> Result<String>

The local key in its own terms: music21’s getLocalKey, which reads a degree against the global key and answers the key it names – V of G is D, and ii of C is d.

With from_dcml the degree is read the lab’s way first, where a minor key’s degrees are written in upper case.

Errors

A degree that names no major or minor triad.