Kronecker's congruence

In mathematics, Kronecker's congruence, introduced by Kronecker, states that

${\displaystyle \Phi _{p}(x,y)\equiv (x-y^{p})(x^{p}-y){\bmod {p}},}$

where p is a prime and Φ_p(x,y) is the modular polynomial of order p, given by

${\displaystyle \Phi _{n}(x,j)=\prod _{\tau }(x-j(\tau ))}$

for j the elliptic modular function and τ running through classes of imaginary quadratic integers of discriminant n.