In mathematics, the Cohen–Hewitt factorization theorem states that if ${\displaystyle V}$ is a left module over a Banach algebra ${\displaystyle B}$ with a left approximate unit ${\displaystyle (u_{i})_{i\in I}}$, then an element ${\displaystyle v}$ of ${\displaystyle V}$ can be factorized as a product ${\displaystyle v=bw}$ (for some ${\displaystyle b\in B}$ and ${\displaystyle w\in V}$) whenever ${\displaystyle \displaystyle \lim _{i\in I}u_{i}v=v}$. The theorem was introduced by Paul Cohen (1959) and Edwin Hewitt (1964).