Nagata–Smirnov metrization theorem

The Nagata–Smirnov metrization theorem in topology characterizes when a topological space is metrizable. The theorem states that a topological space X is metrizable if and only if it is regular and Hausdorff and has a countably locally finite (i.e., σ-locally finite) basis.

Unlike Urysohn's metrization theorem, which provides a sufficient condition for metrization, this theorem provides both a necessary and sufficient condition for a topological space to be metrizable. The theorem is named after Junichi Nagata and Yuriĭ Mikhaĭlovich Smirnov.

See also

• Bing metrization theorem

References

• Munkres, James R. (1975), "Sections 6-2 and 6-3", Topology, Prentice Hall, pp. 247–253, ISBN 0-13-925495-1 .
• Patty, C. Wayne (2009), "7.3 The Nagata–Smirnov Metrization Theorem", Foundations of Topology (2nd ed.), Jones & Bartlett, pp. 257–262, ISBN 9780763742348 .

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