Proving 2+2=4 Using Field Axioms

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Discussion Overview

The discussion revolves around the question of how to prove that 2+2=4 using field axioms. Participants explore definitions and foundational concepts related to numbers and addition, considering both formal definitions and intuitive understandings.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant expresses uncertainty about how to prove 2+2=4 and suggests that field axioms might be necessary.
  • Another participant questions the definitions of 2 and 4, implying that clarity on these definitions is essential for the proof.
  • A different participant references a source, "Foundations of Analysis by Landau," suggesting it may contain relevant information.
  • One participant provides a detailed definition of numbers using set theory, explaining how addition can be defined recursively, ultimately leading to the conclusion that 2+2=4.
  • A beginner participant attempts to present a proof using a different approach but is unsure about the validity of their reasoning.
  • Another participant challenges the previous proof attempts by emphasizing the need for clear definitions of the terms used, arguing that assumptions about basic arithmetic do not constitute a proof.

Areas of Agreement / Disagreement

Participants do not reach a consensus on how to prove 2+2=4, with multiple competing views and approaches presented. There is disagreement regarding the necessity of definitions and the validity of the proposed proofs.

Contextual Notes

The discussion highlights limitations in the assumptions made about basic arithmetic and the definitions of numbers and operations, which remain unresolved.

rafasaur
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I've looked around but haven't found anyway to prove 2+2=4. I'm pretty sure you need to use field axioms, but I just haven't found it yet. Is there a way to do it? Like showing a+a=2a? Or a+b=c? Like 1+1=2. Something like that.

Thanks!
 
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What is the definition of 2? Of 4?
 
rafasaur said:
I've looked around but haven't found anyway to prove 2+2=4.

See Foundations of Analysis by Landau.
 
You just need a definition of 2, of 4 and of +.
Defn: 0 = empty set. 1 = {0}. 2 = {0,1} = {0,{0}}, 3 = {0,1,2} = {0,{0},{0,{0}}},
4 = {0,1,2,3} = {0,{0},{0,{0}}, {0,{0},{0,{0}}}}.
Addition is defined recursively. I.e. first adding one is defined. n + 1 = n union {n}.

i.e. 1+ 1 = {0} union {{0}} = {0,{0}} = 2.
2+1 = 2 union {2} = {0,1} union {2} = {0,1,2} = 3.
3+1 = {0,1,2}+1 = {0,1,2} union {3} = {0,1,2,3} = 4.
Assuming we have defined n+m then n + (m+1) = (n+m)+1.

now you have enough to do it. or keep reading.
So 2 + 2 = (2+1)+1 = 3+1 = 4.

Tata!

Aren’t you glad you asked? Basically it seems 4 = ((1+1)+1)+1. and 2 = (1+1).
so 2+2 = (1+1)+(1+1), so it boils down to associativity of +.
 
(1+1+1+1)=1+1+1+1
(1+1)+(1+1)=4(1)
2+2=4

Does that work? Sorry I'm a beginner when it comes to proofs.
 
You haven't said why "1+ 1+ 1+ 1" would be equal to "4(1)" or why 4(1) would be equal to 4. That was Mathwonk's point- this whole thing depends upon exactly how you define "+", "1", "2", and "4". You have just assumed basic arithmetic without giving any definitions. That is no different from just assuming that 2+ 2= 4.
 

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