Monotonically normal space

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

This is a variation of normality. View other variations of normality

This article or section of article is sourced from:Wikipedia

Definition

Definition with symbols

A topological space $X$ is termed monotonically normal if it is a T1 space (i.e., all points are closed) and there exists an operator $G$ from ordered pairs of disjoint closed sets to open sets, such that:

1. For any disjoint closed subsets $A,B$, $G(A,B)$ contains $A$ and its closure is disjoint from $B$
2. If $A\subseteq A^{\prime }$ and $B^{\prime }\subseteq B$ with all four sets being closed, $A$ disjoint from $B$, and $A^{\prime }$ disjoint from $B^{\prime }$, we have:

$G(A,B)\subseteq G(A^{\prime },B^{\prime })$

This is the monotonicity condition. Such an operator $G$ is termed a monotone normality operator.

Relation with other properties

Stronger properties

property	quick description	proof of implication	proof of strictness (reverse implication failure)	intermediate notions
Metrizable space	underlying topology of a metric space	metrizable implies monotonically normal	monotonically normal not implies metrizable	Elastic space, Protometrizable space|FULL LIST, MORE INFO
Ordered field-metrizable space	underlying topology of a space with a metric taking values in an ordered field	ordered field-metrizable implies monotonically normal	monotonically normal not implies ordered field-metrizable	|FULL LIST, MORE INFO
Linearly orderable space	order topology from a linear ordering on a set	linearly orderable implies monotonically normal	monotonically normal not implies linearly orderable	|FULL LIST, MORE INFO
Elastic space		elastic implies monotonically normal	monotonically normal not implies elastic	|FULL LIST, MORE INFO
Closed sub-Euclidean space		(via metrizable)	(via metrizable)	Elastic space, Metrizable space, Protometrizable space|FULL LIST, MORE INFO
Manifold		(via metrizable)	(via metrizable)	Elastic space, Metrizable space, Protometrizable space|FULL LIST, MORE INFO

Weaker properties

property	quick description	proof of implication	proof of strictness (reverse implication failure)	intermediate notions
Normal space	any two disjoint closed subsets are separated by disjoint open subsets	monotonically normal implies normal	normal not implies monotonically normal	Collectionwise normal space, Hereditarily collectionwise normal space, Hereditarily normal space|FULL LIST, MORE INFO
Hereditarily normal space	every subspace is a normal space	monotonically normal implies hereditarily normal	hereditarily normal implies monotonically normal	Hereditarily collectionwise normal space|FULL LIST, MORE INFO
Collectionwise normal space	every discrete collection of closed subsets can be separated by disjoint open subsets	monotonically normal not implies collectionwise normal	collectionwise normal not implies monotonically normal	Hereditarily collectionwise normal space|FULL LIST, MORE INFO
Hereditarily collectionwise normal space	every subspace is collectionwise normal	monotonically normal implies hereditarily collectionwise normal	hereditarily collectionwise normal not implies monotonically normal	|FULL LIST, MORE INFO

Incomparable properties

• Perfectly normal space

Metaproperties

Hereditariness

This property of topological spaces is hereditary, or subspace-closed. In other words, any subspace (subset with the subspace topology) of a topological space with this property also has this property.
View other subspace-hereditary properties of topological spaces

Any subspace of a monotonically normal space is monotonically normal. For full proof, refer: Monotone normality is hereditary