In this document: http://cims.nyu.edu/~kiryl/teaching/aa/les092603.pdf
The ordered pair notation is used but it is never explained what it means.
Corollary: Let p be a prime. Then n^(p−1) ≡ 1 mod p for any integer n ≥ 1 with (n, p) = 1.
Does anyone know what (a,b) signifies in this context?