Question about the axioms of set theory

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SUMMARY

The discussion centers on the axioms of set theory as applied to the structure U = {a, b} with the membership relations a in b and b in a. The directed graph representation indicates that the structure satisfies the axioms of Extensionality, Pairing, and Union, but fails the Foundation axiom due to the circular membership. Participants emphasize the need for clearer justifications in symbolic form to ensure full marks in academic evaluations.

PREREQUISITES
  • Understanding of set theory axioms, specifically Extensionality, Foundation, Pairing, and Union.
  • Familiarity with directed graphs and their representation of membership relations.
  • Basic knowledge of symbolic logic for formal justification of axioms.
  • Experience with academic writing standards in mathematics for clear communication of concepts.
NEXT STEPS
  • Research the implications of the Foundation axiom in set theory.
  • Learn how to construct directed graphs for various set structures.
  • Study formal symbolic representations of set theory axioms.
  • Explore grading criteria for mathematics assignments to improve justification techniques.
USEFUL FOR

This discussion is beneficial for students of mathematics, particularly those studying set theory, educators grading assignments, and anyone interested in the formal aspects of mathematical logic and justification.

cragar
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Homework Statement


For each structure, draw a directed graph representing the membership relation. Then determine which of the following axioms is satisfied by the structure: Extensionality, Foundation, Pairing, Union
U= {a,b} a in b , and b in a

The Attempt at a Solution


The directed graph would be an arrow from a to b and then an arrow from b to a.
This fails foundation because a can't be in b and b can't be in a.
It satisfies Extensionality because a is a member of b and vice versa.
it satisfies pairing and union

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I agree with your conclusions, but your justification of them is very terse and doesn't make it clear how the axioms that fail do so. Hence it may not get full marks from the lecturer. I would suggest writing out the justifications more fully, in symbolic form rather than prose. In particular, justifying that Pairing is not violated takes several steps, as you need to show that the set {a} is part of the structure.
 

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