It's bad practice, but I love how optimized it is.

excelente me sorprende a veces la capcidad en la que los codigos de php se pueden comprimir a tal punto en que solo ocupan una sola linea de codigo.

Yes, it's a good solution in one line, but it does not use memory effective. We have a memory limit exception if parameter $n is huge number (for example, 1 Gb of memory is not enough if $n = 17 millions).

English version of docs, sorry =]
https://www.php.net/manual/en/function.gmp-prob-prime.php

lol it break formatting =[

Built-in fast PHP function for this purpose, (no GMP, not pass tests)
PHP Docs: https://www.php.net/manual/ru/function.gmp-prob-prime.php
Example:

function is_prime(int $n): bool {

switch (gmp_prob_prime($n)) {

case 0: return false;

default: return true;

}

}

Yeah, I'd like to know as well