User:Lériendil/On the primes
The way each of the primes tends to behave within xenharmony is largely defined by the numbers that neighbor it. Every prime (bar 2) splits some superparticular in half, and that prime's neighbors are twice the numerator and denominator of that superparticular. Other isoharmonic sequences, such as those which differ by 2, 3, or 4, can also be used, but are much less likely to split intervals that belong to significantly lower prime-limits. However, the process of splitting superparticulars in half induces primes 2 and 3 necessarily, and so isoharmonies of deltas 2 and 3 are fundamental to no-twos or no-threes structures.
Modularity classes
Primes belonging to different residue classes modulo 4, 6, and 10 have meaningfully different properties in relation to splitting isoharmonies.
Modulo 4, primes (apart from 2) can be 4k+1 or 4k-1.
- 4k+1 primes (5, 13, 17, ...) we call "upper".
- 4k-1 primes (3, 7, 11, 19, ...) we call "lower".
- Upper × upper = lower × lower = upper. Upper × lower = lower.
Modulo 6, primes (apart from 2 and 3) can be 6k+1 or 6k-1.
- 6k+1 primes (7, 13, 19, ...) we call "cold".
- 6k-1 primes (5, 11, 17, ...) we call "hot".
- 3 is neutral, but can be grouped with the cold primes by convention.
- Cold × cold = hot × hot = cold. Cold × hot = hot.
Modulo 10, primes (apart from 2 and 5) can be 10k+1, 10k+3, 10k-3, or 10k-1.
- 10k±1 primes (11, 19, 29, 31, ...) we call "telluric".
- 10k±3 primes (3, 7, 13, 17, 23, ...) we call "thalassic".
- 5 is neutral, but can be grouped with the telluric primes by convention.
- Telluric × telluric = thalassic × thalassic = telluric. Telluric × thalassic = thalassic.
prime 15
