local lemma Nakayama's lemma Poincaré's lemma Riesz's lemma Schur's lemma Schwarz's lemma Sperner's lemma Urysohn's lemma Vitali covering lemma Yoneda's...

theorem (to do) Ultrafilter lemma Ultraparallel theorem Urysohn's lemma Van der Waerden's theorem Wilson's theorem Zorn's lemma Bellman–Ford algorithm (to...

axiom of choice, in which all sets of real numbers are measurable. Urysohn's lemma (UL) and the Tietze extension theorem (TET) are independent of ZF+ACω:...

disjoint closed sets can be separated by a continuous function; this is Urysohn's lemma.) X is completely normal, or T5 or completely T4, if it is T1 and if...

perhaps the single most important result in general topology (along with Urysohn's lemma). The theorem is also valid for topological spaces based on fuzzy sets...

problems, invented magnetotellurics Pavel Urysohn, developed the metrization theorems, Urysohn's Lemma and Fréchet–Urysohn space in topology Nicolay Vasilyev...

topology), invented magnetotellurics Pavel Urysohn, developed the metrization theorems, Urysohn's Lemma and Fréchet–Urysohn space in topology Nicolay Vasilyev...

and physical research. Russian mathematicians Pavel Alexandrov and Pavel Urysohn were the first of several in 1923. Between 1926 and 1930, Alexandrov regularly...

metrizable spaces (or more generally first-countable spaces or Fréchet–Urysohn spaces), sequences usually suffices to characterize, or "describe", most...