https://en.wikipedia.org/wiki/Function_(music)
Read the whole article. Btw, it assumes meantone temperament.

Pythagorean tuning is schismic (until 665 edo when schisma becomes a step), so the theory is different (diminished and augmented intervals are the 5-limit consonances = 317.595 cents, which is almost pure min3rd is Pythagorean augmented second and 384.360 cents, almost major third is Pythagorean diminished fourth).

Schismic, meantone and their difference (diashismic) and their sum (pythagorean comma) meet in 12 equal only (this can lead to potentially confusing or wrong notation systems)