Show disjoint sets are mutually separated?

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SUMMARY

This discussion addresses the proof that any two disjoint nonempty open sets and any two disjoint nonempty closed sets are mutually separated. The initial assumption that disjoint sets can share a boundary point leads to a contradiction, as demonstrated with the example of sets A = (0,1) and B = (1,2). The boundary point 1 is not contained in either set, reinforcing the conclusion that disjoint sets do not share boundary points. The reasoning applies similarly to closed sets, confirming the mutual separation property.

PREREQUISITES
  • Understanding of open and closed sets in topology
  • Familiarity with boundary points and their properties
  • Basic knowledge of set theory and disjoint sets
  • Experience with mathematical proofs and logical reasoning
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  • Study the properties of open and closed sets in topology
  • Learn about boundary points and their significance in set theory
  • Explore examples of disjoint sets and their mutual separation
  • Investigate the implications of the separation axioms in topology
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Mathematics students, particularly those studying topology, set theory, or real analysis, will benefit from this discussion.

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Homework Statement



Show that any two disjoint nonempty open sets are mutually separated.

Show that any two disjoint nonempty closed sets are mutually separated.

Homework Equations





The Attempt at a Solution



Let A and B be two disjoint nonempty open sets:

Assume A and B share a boundary point.

That boundary point exists in A intersect B. If the sets are disjoint, they can't intersect so this is a contradiction.

Similar idea for closed sets.

Is this correct?
 
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No. What if A = (0,1) and B = (1,2). They both have 1 as a boundary point but it isn't in either.
 

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