# Contents

## Definition

Let $f : X \to Y$ be a morphism of schemes. Let $\Delta_f: X \to X \times_Y X$ be the diagonal map. We say that $f$ is quasi-separated if $\Delta_f$ is a quasicompact morphism.

A scheme $X$ is quasi-separated if the morphism $X \to Spec\, \mathbf{Z}$ is quasi-separated, i.e. $\Delta:X\to X\times X$ is quasicompact. Every quasi-separated scheme is semiseparated.

## Properties

Every separated morphism of schemes is quasi-separated; every monomorphism of schemes is separated hence also quasi-separated.

## References

Revised on August 14, 2014 19:42:45 by Bordieck? (1.219.246.235)