Definition 29.23.1. Let $f : X \to S$ be a morphism.

We say $f$ is

*open*if the map on underlying topological spaces is open.We say $f$ is

*universally open*if for any morphism of schemes $S' \to S$ the base change $f' : X_{S'} \to S'$ is open.

Definition 29.23.1. Let $f : X \to S$ be a morphism.

We say $f$ is

*open*if the map on underlying topological spaces is open.We say $f$ is

*universally open*if for any morphism of schemes $S' \to S$ the base change $f' : X_{S'} \to S'$ is open.

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