For any two points 
there exists two open sets 
and 
such that 
and 
, and 
and 
. A space satisfying this axiom is known as a T1-space.
T_1-Separation Axiom
See also
Hausdorff Axioms, Separation Axioms, T1-SpaceThis entry contributed by Margherita Barile
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Cite this as:
Weisstein, Eric W., with contributions by Margherita Barile. "T_1-Separation Axiom." From MathWorld--A Wolfram Resource. https://mathworld.wolfram.com/T1-SeparationAxiom.html