Urysohn's Metrization Theorem/Historical Note

Historical Note on Urysohn's Metrization Theorem

This form of Urysohn's Metrization Theorem was actually proved by Andrey Nikolayevich Tychonoff in $1926$.

What Urysohn had shown, in a posthumous $1925$ paper, was that every second-countable normal Hausdorff space is metrizable.