The statement that a and b are congruent modulo n: written
a = b (mod n), or a ≡ b (mod n), and meaning n divides a - b. A
relation between integers with the modulus written once at the end, as mathematics
writes it — not the remainder operator a mod n, which is a number, and which the
reference this follows refuses to write in this sense at all. The modulus may be any
integer: modulo 0 it is equality, and its sign is immaterial, exactly as in
n divides a - b. A statement about integers: NaN elsewhere.
https://github.com/asc-community/AngouriMath/issues/1409