Semiregular space

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This article defines a property of topological spaces: a property that can be evaluated to true/false for any topological space|View a complete list of properties of topological spaces


A semiregular space is a topological space Xsatisfying the following equivalent conditions:

  1. The regular open subsets (these are subsets that equal the interior of their closure) form a basis for the space.
  2. For any x \in X and any open subset V \subseteq X containing x, there exists a regular open subset U of X containing x and contained in V.

Note that regular open is not the same as being open and regular in the subspace topology. For the notion defined using that, see locally regular space.

Relation with other properties

Stronger properties

Property Meaning Proof of implication Proof of strictness (reverse implication failure) Intermediate notions
regular space regular implies semiregular semiregular not implies regular