Second Countable Topology
A topological space is second countable if it has a countable topological basis.
See also
Topological Basis, Topological SpaceExplore with Wolfram|Alpha
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Cite this as:
Weisstein, Eric W. "Second Countable Topology." From MathWorld--A Wolfram Resource. https://mathworld.wolfram.com/SecondCountableTopology.html