Cardinality of Real Numbers & Irrationals: Prove They're Equal

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    Cardinality
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Discussion Overview

The discussion revolves around proving that the set of irrational numbers has the same cardinality as the set of real numbers. Participants explore various approaches to this proof, including the use of bijections and cardinal arithmetic.

Discussion Character

  • Exploratory, Technical explanation, Debate/contested

Main Points Raised

  • One participant suggests constructing a bijection by selecting a countable set within the irrationals and defining a bijection that acts as the identity outside of that set.
  • Another participant proposes using arithmetic of cardinal numbers as a method to demonstrate the equality of cardinalities.
  • A third participant notes that the reals can be viewed as a disjoint union of rationals and irrationals, referencing a prior suggestion made by another participant.

Areas of Agreement / Disagreement

Participants present multiple competing views on how to approach the proof, indicating that the discussion remains unresolved.

Contextual Notes

Some assumptions about the nature of the sets and the definitions of cardinality may be implicit in the discussion, and the effectiveness of the proposed methods has not been established.

mathgeek808
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Need help with this proof:
Prove that the set of irrational numbers has the same cardinality as the set of real numbers.
 
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I would do this by a bijection. Pick a countable set A in the irrational numbers (think cosets if you can't come up with an example). Then construct a bijection that is the identity outside of A
 
The reals are the disjoint union of rationals and irrationals. Take this back to Hurkyl's suggestion.
 

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