A continuous real-valued function on a closed subspace A of a normal space X extends to a continuous function on all of X, preserving the range [a, b]. Equivalently characterises normality. Tietze 1915; modern proof via the Urysohn lemma…
A continuous real-valued function on a closed subspace A of a normal space X extends to a continuous function on all of X, preserving the range [a, b]. Equivalently characterises normality. Tietze 1915; modern proof via the Urysohn lemma…