Math 2.0

General topology Proposition

Cantor set is closed

Builds on Cantor setIntersection of closed sets is closedClosed set

Statement

The Cantor set C=⋂n≥0CnC = \bigcap_{n \ge 0} C_n is a closed subset of ℝ\mathbb{R}.

Remarks

Proof: each CnC_n is a union of 2n2^n closed intervals, so it is closed. An intersection of closed sets is closed. Since C⊆[0,1]C \subseteq [0, 1], the set CC is also bounded, and thus compact by the Heine–Borel theorem. Each endpoint of an interval of some CnC_n lies in CC. For example, 13\tfrac{1}{3} and 23\tfrac{2}{3} are in CC.

Reading path

To understand this page from the ground up, read these 43 pages in order. The foundations come first.

  1. Cantor set example
  2. Element definition
  3. Proposition concept
  4. Real numbers object
  5. Set definition
  6. Conjunction definition
  7. Disjunction definition
  8. Implication definition
  9. Negation definition
  10. Predicate definition
  11. Empty set object
  12. Family of sets definition
  13. Ordered pair definition
  14. Intersection definition
  15. Union definition
  16. Biconditional definition
  17. Truth table concept
  18. Existential quantifier definition
  19. Universal quantifier definition
  20. Cartesian product definition
  21. Propositional logic concept
  22. Subset definition
  23. Intersection of a family of sets definition
  24. Union of a family of sets definition
  25. Uniqueness quantifier definition
  26. Binary relation definition
  27. Universal set definition
  28. Topological space definition
  29. Tautology definition
  30. Complement definition
  31. Function definition
  32. Logical equivalence definition
  33. Metric space definition
  34. De Morgan's laws statement
  35. Open ball definition
  36. De Morgan's laws for sets statement
  37. Metric topology definition
  38. Open set definition
  39. Open sets of a metric space statement
  40. Closed set definition
  41. Union of open sets is open statement
  42. Intersection of closed sets is closed statement
  43. Cantor set is closed statement

Further reading

  1. Web https://en.wikipedia.org/wiki/Cantor_set, Topological and analytical properties
About this page
Tag01VT24J1SD
URIm2://01VT24J1SD
Kindstatement, proposition
WritingW0 stub
MSC54F65
StatusThis copy of the site has no build data. Run m2 status 01VT24J1SD.
UsesCantor set, Intersection of closed sets is closed, Closed set

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