Using the Compactness Theorem to Show Distance Between c and d

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SUMMARY

The discussion focuses on utilizing the Compactness Theorem to demonstrate that two elements, c and d, are significantly distant from each other within a logical framework. The participants reference the textbook "A Mathematical Introduction to Logic" by Herbert B. Enderton as a foundational resource. Specifically, the approach involves constructing sentences phi_n that assert the distance between c and d is at least n, and applying the Compactness Theorem to these sentences to establish the existence of an elementarily equivalent structure B that is not connected.

PREREQUISITES
  • Understanding of the Compactness Theorem in logic
  • Familiarity with elementarily equivalent structures
  • Knowledge of logical sentences and their construction
  • Basic concepts from the textbook "A Mathematical Introduction to Logic" by Herbert B. Enderton
NEXT STEPS
  • Study the Compactness Theorem in detail
  • Explore the concept of elementarily equivalent structures
  • Learn how to construct logical sentences to express distance between elements
  • Review examples from "A Mathematical Introduction to Logic" by Herbert B. Enderton
USEFUL FOR

Logicians, mathematics students, and anyone interested in the application of the Compactness Theorem in demonstrating properties of logical structures.

Soi-Arse
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How to write down the sentences saying that c and d are far apart?

And what's the purpose to do so for showing that there is an elementarily equivalent structure B that is not connected.

Actually this is a question from the logic textbook " A mathematical introduction to logic " by Herbert B. Enderton.

I post this question here since it relates to pure logic and I hope someone can give me any advice.

Thank you.

Sincerely
 
Last edited:
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For each n, let phi_n be the sentence saying that the distance between c and d is at least n. Now try applying the compactness theorem to this set of sentences.
 

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