[topology] new kind of separation axiom? where does it fit in?

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SUMMARY

The discussion centers on a new separation axiom in topology, specifically regarding a topological space X defined as T1. The axiom states that for any two closed subsets A and B, there exists an open set U such that B is contained in U and A is disjoint from U. Participants clarify the conditions of the axiom, confirming that A and B must be disjoint, and explore the implications of using the complement of A as U.

PREREQUISITES
  • Understanding of T1, T2, T3, and T4 separation axioms in topology
  • Familiarity with the concept of open and closed sets in topological spaces
  • Knowledge of the Urysohn theorem and completely regular spaces
  • Basic principles of set theory, particularly regarding set complements and intersections
NEXT STEPS
  • Research the implications of the new separation axiom on existing topological frameworks
  • Study the properties and applications of T1, T2, T3, and T4 spaces in depth
  • Explore the Urysohn theorem and its relevance to completely regular spaces
  • Investigate other separation axioms and their relationships within topology
USEFUL FOR

Mathematicians, particularly those specializing in topology, educators teaching advanced mathematics, and students seeking to deepen their understanding of separation axioms and their applications.

nonequilibrium
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Hello,

Just out of curiosity, where would following "separation axiom" fit in?

Assume a topological space X is T1. We call X okay if for any two closed subsets A and B, there exists an open set U such that [itex]B \subset U[/itex] and [itex]A \cap U = \emptyset[/itex].

So far I'm only acquainted with the T1, T2, T3 and T4 axioms (and the notion of completely regular in relation to the Urysohn theorem).
 
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You mean A and B disjoint right??

Can't you always take [itex]U=X\setminus A[/itex]??
 
Haha...

(and yes I meant A and B disjoint)

It seems I hadn't thought this one true :) thanks a lot!
 

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