Using the Compactness Theorem to Show Distance Between c and d

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In summary, the conversation discusses how to write sentences that demonstrate that two elements, c and d, are far apart. This is related to showing that an elementarily equivalent structure B exists that is not connected. The question is from a logic textbook and the poster is seeking advice and help on this topic. The suggestion is to use the compactness theorem by creating sentences that state the distance between c and d is at least n for each n.
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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
 
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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.
 

Related to Using the Compactness Theorem to Show Distance Between c and d

1. What is a compactness problem?

A compactness problem is a mathematical question that involves determining whether a given set or space is compact. Compactness is a property of a set or space that describes how close together the points are. In simpler terms, it is a measure of how much space the set or space takes up.

2. Why is compactness important in science?

Compactness is important in science because it helps us understand and describe the behavior of physical systems, such as the behavior of particles in a confined space. It also has applications in various fields of science, including physics, chemistry, and biology.

3. What are some examples of compactness problems?

Some examples of compactness problems include the question of whether a given set of numbers is bounded, whether a given set of functions has a limit, and whether a given space is path-connected. These are just a few examples, as there are many different types of compactness problems in various fields of science.

4. How are compactness problems solved?

Compactness problems are typically solved using mathematical techniques and tools, such as topology, analysis, and algebra. The specific approach may vary depending on the type of problem, but the goal is always to prove whether the set or space in question is compact or not.

5. What are the implications of solving a compactness problem?

Solving a compactness problem can have various implications, depending on the context. It can help us better understand the behavior of physical systems and make predictions about their behavior. It can also lead to the development of new theories and concepts in science, as well as practical applications in fields such as engineering and technology.

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