Useful information. :) Thanks!

I can see a lot of thought went into this. Hence my question...

Why all the comments? Why not just use descriptive variable names? The code would be much more readable.

Description should be language-agnostic

well, the wording is still totally awful, for non musicians... XD

Intervals are named for the distance, first note inclusive, between the lower note and the higher note. >>> This distance is measured not in semitones or whole tones, but rather in note names spanned. <<<

It measures Degree intervals (of the Major Scale), regardless of the Pitch intervals between degrees, starting with value 1 for the zero distance interval. As author mentioned, each letter represents such degree. Octave numbers are added to be able to measure degree intervals across octaves.

Melodic and harmonic intervals are named for the distance from one letter name to the other letter name, first and last note inclusive

('A0', 'A0') => 1 (unison)
('A0', 'B0') => 2 (second)

This is standard convention for musicians. The ordinal number is then paired with a modifier such as 'major', 'minor', 'perfect', etc... but that is beyond the scope of this kata

Your test ('A0', 'B0', 2). From 'A0' to 'B0' or 1 note(!), or 2 semitones.
('F4', 'B4', 4). From 'B4' to 'F4' or 4 notes(!), or 6 semitones.
So what we searching???

Wut

Thank you.

Hi! The unit is neither tones nor semitones, but rather letter note names. This is the standard way to refer to melodic and harmonic intervals in every music theory class I have taken.

C to a E has four semitones (or two whole tones), and is called a 3rd, specifically a major third, because it comprehends three note names.

E to G has three semitones, or 1.5 whole tones, but is also called a 3rd, specifically a minor third, because it also comprehends three note names.

I've added a note in the description to emphasize this concept; hopefully it will be helpful.

Hi,

The unit used for "intervals" is not given. Tones ? semi tones? ...? Currently, someone not familiar with music theory will have to retro-engineer the logic to solve the kata.

Cheers