Filtered algebra

In mathematics, a filtered algebra is a generalization of the notion of a graded algebra. Examples appear in many branches of mathematics, especially in homological algebra and representation theory.

A filtered algebra over the field ${\displaystyle k}$ is an algebra ${\displaystyle (A,\cdot )}$ over ${\displaystyle k}$ that has an increasing sequence ${\displaystyle \{0\}\subseteq F_{0}\subseteq F_{1}\subseteq \cdots \subseteq F_{i}\subseteq \cdots \subseteq A}$ of subspaces of ${\displaystyle A}$ such that

${\displaystyle A=\bigcup _{i\in \mathbb {N} }F_{i}}$

and that is compatible with the multiplication in the following sense:

${\displaystyle \forall m,n\in \mathbb {N} ,\quad F_{m}\cdot F_{n}\subseteq F_{n+m}.}$