A topological space fulfilling the 
-axiom: 
fulfils the T1-separation
axiom and is normal. In the terminology of Alexandroff and Hopf (1972), 
-space are called Tietze spaces.
T_4-Space
See also
Hausdorff Axioms, Separation Axioms, T0-Space, T1-Separation Axiom, T1-Space, T2-Space, T3-SpaceThis entry contributed by Margherita Barile
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References
Alexandroff, P. and Hopf, H. Topologie, Vol. 1. New York: Chelsea, 1972.Cite this as:
Barile, Margherita. "T_4-Space." From MathWorld--A Wolfram Web Resource, created by Eric W. Weisstein. https://mathworld.wolfram.com/T4-Space.html