Abbreviation: Haus

A \emph{Hausdorff space} or \emph{$T_2$-space} is a topological spaces $\mathbf{X}=\langle X,\Omega(\mathbf{X})\rangle$ such that

for every pair of distinct points in the space, there is a pair of disjoint open sets containing each point: $x,y\in X\Longrightarrow\exists U,V\in\Omega(\mathbf{X})[x\in U\mbox{ and }y\in V\mbox{ and }U\cap V=\emptyset]$

Let $\mathbf{X}$ and $\mathbf{Y}$ be Hausdorff spaces. A morphism from $\mathbf{X}$ to $\mathbf{Y}$ is a function $f:X\rightarrow Y$ that is \emph{continuous}:

$V\in\Omega(\mathbf{Y})\Longrightarrow f^{-1}[V]\in\Omega(\mathbf{X})$

Example 1:

Remark: The properties given above use an $(\mathcal{E},\mathcal{M})$ factorization system with $\mathcal{E}=$ surjective morphisms and $\mathcal{M}=$ embeddings.

Compact Hausdorff spaces

Completely Hausdorff spaces

T1-spaces

see also http://www.wikipedia.org/wiki/Hausdorff_space

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