Schur-Zassenhaus theorem (source code)

= Schur-Zassenhaus theorem
{c}

A finite <normal subgroup> whose order is coprime to its index has a <group complement>: if $N\triangleleft G$ is a <Hall subgroup>, then $G=NH$ and $N\cap H=1$ for some subgroup $H$. Complement conjugacy holds when either $N$ or $G/N$ is solvable; the existence assertion does not require that extra hypothesis.