Definition of Strong and Weak form of a theorem

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Discussion Overview

The discussion revolves around the definitions and implications of strong and weak forms of theorems in mathematics. Participants explore the nuances of these terms, including their relationships to hypotheses and results, as well as the potential for exceptions in their application.

Discussion Character

  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant suggests that a theorem p is considered stronger than q if p implies q, while q is weaker if it implies p.
  • Another participant agrees but notes that generally, a strong version requires more hypotheses than a weak version, yet proves a stronger result.
  • There is mention of exceptions, such as the equivalence of induction and strong induction, which complicates the definitions of strong and weak forms.
  • A participant questions whether dropping or replacing a hypothesis while maintaining the same result constitutes strengthening or weakening, expressing confusion about how this aligns with the initial definitions.
  • Another participant asserts that a theorem with fewer assumptions is "stronger" or "more general," but suggests that the terms may not carry significant information.

Areas of Agreement / Disagreement

Participants express varying interpretations of what constitutes strong and weak forms, with no consensus reached on the definitions or implications. Some agree on general principles, while others highlight exceptions and nuances that complicate the discussion.

Contextual Notes

Participants acknowledge that the definitions of strong and weak forms may depend on specific contexts and that there are exceptions to the general rules discussed.

JFo
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Could someone explain to me what it means for a theorem to be a strong(er) form or a weak(er) form of another theorem?

I've heard these terms used over and over, but never bothered to ask. If I had to guess at a definition, I'd say that if q is a theorem then we say p is stronger if p implies q. Similarly p is weaker if q implies p. Am I close?
 
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Yes. Generally - aren't there always exceptions in mathematics.

As a general rule the strong version will need more hypotheses than the weak version, but correspondingly prove a result that is stronger (and implies the weaker version).

This is not always the case, as there is at least on situation where the strong and weak version actually are equivalent: induction and strong induction are the same, but phrased differently so that one seems like a stronger (more powerful) result.
 
Thanks. I know it's mostly semantics, but I couldn't find a definition, or even a description, anywhere.
 
So if we have a theorem, and are then able to show that we can drop one of the hypotheses (or replace it with a weaker hypothesis) and still obtain the same result, would that be considered "strengthening" or "weakening"

Intuitively I would think strengthening, but then I don't know how that fits in with the quasi-definition given above since we have less hypotheses but the result remains unchanged. Or is this a different meaning of strong/weak entirely?
 
JFo said:
So if we have a theorem, and are then able to show that we can drop one of the hypotheses (or replace it with a weaker hypothesis) and still obtain the same result, would that be considered "strengthening" or "weakening"

Intuitively I would think strengthening, but then I don't know how that fits in with the quasi-definition given above since we have less hypotheses but the result remains unchanged. Or is this a different meaning of strong/weak entirely?

The theorem that assumes less in the hypothesis is "stronger" or "more general". I wouldn't worry too much about what these terms exactly mean though, since they don't carry much information.
 

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