Reading through the rest of GNU Multiprecisions MPZ sublibrary, I see:
* Wrappers around initialization & conversion from
- doubles
- another MPZ struct
- signed longs
- unsigned longs
* Initialization multiple MPZs via variadic arguments
* Initialize a single MPZ struct by allocating its digits or set a dummy value
* Divide 1 by a given MPZ via `mpz_gcdext` with postprocessing
* Inclusive bitwise-or, reallocating where ncessary as it turns it into a bitwise-and operation
1/?