Open map

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Created quickly, just to document the concept

A closed map is a thing too and is defined similarly.

Definition

Let $(X,\mathcal{ J })$ and $(Y,\mathcal{ K })$ be topological spaces and let $f:X\rightarrow Y$ be a map (not necessarily continuous - just a map between $X$ and $Y$ considered as sets), then we call $f$ an open map if:

• $\forall U\in\mathcal{J}[f(U)\in\mathcal{K}]$ - that is, that the images (under $f$) of all open sets of $(X,\mathcal{ J })$ are open in $(Y,\mathcal{ K })$