Metrizable space

This article defines a property of topological space that is pivotal (viz important) among currently studied properties of topological spaces

This article is about a basic definition in topology.
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Definition

Symbol-free definition

A topological space is said to be metrizable if it occurs as the underlying topological space of a metric space.

Relation with other properties

Stronger properties

• Completely metrizable space
• sub-Euclidean space
• closed sub-Euclidean space
• Manifold

Weaker properties

• Ordered field-metrizable space
• Elastic space
• Monotonically normal space
• Perfectly normal space
• Regular Lindelof space
• Paracompact Hausdorff space
• 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 metrizable space is metrizable. In fact, the subspace topology coincides with the topology induced from the metric obtained on the subset ,by restricting the metric from the whole space.

Products

This property of topological spaces is closed under taking finite products

A finite product of metrizable spaces is again metrizable. In fact, we can take the metric as, say, the sum of metric distances in each coordinate. More generally, we could use any of the $L^p$-norms ($1\le p\le \mathrm{\infty }$) to combine the individual metrics.