Urysohn lemma(redirected from Urysohn's lemma)
Also found in: Wikipedia.
Urysohn lemma[′u̇r·ē‚zōn ‚lem·ə]
If A and B are disjoint, closed sets in a normal space X, there is a real-valued function ƒ such that 0 ≤ ƒ(x) ≤ 1 for all x ∈ X, and ƒ (A) = 0 and ƒ (B) = 1.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.