When Does A Set Minus B Equal B Minus A?

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SUMMARY

The discussion centers on the conditions under which the set difference A - B equals B - A. The primary conclusion is that A - B = B - A holds true if and only if the sets A and B are equal (A = B). The user seeks guidance on how to approach the proof without receiving the entire solution, indicating a desire to understand the underlying principles of set theory. Key equations referenced include A - B = A ∩ B^c and B - A = B ∩ A^c.

PREREQUISITES
  • Understanding of set theory, specifically set operations like intersection and set difference.
  • Familiarity with the notation of complements in set theory (e.g., B^c).
  • Knowledge of basic proof techniques in mathematics.
  • Ability to manipulate and reason about logical statements involving sets.
NEXT STEPS
  • Study the properties of set operations, particularly focusing on set equality and set difference.
  • Learn about the proof techniques used in set theory, including direct proof and proof by contradiction.
  • Explore examples of set identities to solidify understanding of A - B and B - A.
  • Investigate the implications of set equality in various mathematical contexts.
USEFUL FOR

Students of mathematics, particularly those studying set theory, as well as educators looking to enhance their understanding of set operations and proofs.

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Homework Statement



For what conditions on sets A and B does A-B = B-A hold?

Homework Equations



A - B = A n B^c
B - A = B n A^c

The Attempt at a Solution



I know that A = B is the answer, but I just don't know where to start...please don't give me the whole proof, I want to figure it out myself. I just need a hint or an idea of where to start.
 
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Start with: If A=B, show A-B = B-A (this should be easy)

Then suppose A-B = B-A. If a \in A you need to prove a \in B and vice versa (the vice versa part comes immediately from the symmetry of the problem if you want to be suave about it)
 

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