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G-delta set

In topology, X, a G-delta set (or G_δ set) is a countable intersection of open sets. In metrizable spaces, every closed set is a G_δ set.

The complement of a G_δ set is an F_σ. In a metrizable space, every open set is an F_σ set.

Referenced By

Boundary (topology) | Completely T4 space | Completely normal Hausdorff space | Completely normal regular space | Completely normal space | Contractible | Cover (set theory) | Cover (topology) | F-sigma set | First countable | Interior (topology) | List of general topology topics | List of mathematical topics (G-I) | List of mathematical topics (G-Z) | Local base | Neighborhood (topology) | Neighbourhood (topology) | Normal Hausdorff space | Normal regular space | Normal space | Open cover | Partition of unity | Partitions of unity | Perfectly T4 space | Perfectly normal Hausdorff space | Perfectly normal regular space | Perfectly normal space | Punctured neighborhood | Punctured neighbourhood | Regular open set | Relatively compact | Second countable | T4 space | T5 space | Topological interior | Topological neighborhood | Topological neighbourhood | Topology Glossary

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This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "G-delta set".

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