Is it true for all n, Natural number?

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Discussion Overview

The discussion revolves around the validity of a predicate P(n) for all natural numbers n, given that P(1) is true and that if P(k) is true, then P(k+2) is also true. Participants explore whether this implies that P(n) holds for all natural numbers or just for a subset of them, particularly odd numbers.

Discussion Character

  • Debate/contested

Main Points Raised

  • William questions whether P(n) is true for all natural numbers based on the given conditions.
  • One participant suggests that the principle of induction applies, indicating that if P(n) is true for a natural number, it can be deduced for subsequent numbers.
  • Another participant argues that P(n) may only be true for odd natural numbers, citing a potential limitation in the original premise.
  • Some participants mention the possibility of constructing a counterexample, where P(n) holds for odd numbers but not for even numbers.
  • There is a discussion about the nature of counterexamples and whether they effectively demonstrate the limitations of the predicate P(n).
  • One participant emphasizes the existence of properties unique to odd numbers that do not apply to even numbers, suggesting that these could be shown through induction.

Areas of Agreement / Disagreement

Participants express differing views on whether P(n) is true for all natural numbers, with some asserting it is not and others suggesting it could depend on the construction of N. The discussion remains unresolved, with multiple competing perspectives presented.

Contextual Notes

Participants note that the validity of P(n) may depend on how the natural numbers are defined or constructed, indicating potential limitations in the assumptions made about P(n).

Willy_Will
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Hello all,

Another quick question for the number theory gurus here:

Let P(n) predicate, n Natural number. Suppose that P(n) satisfies that P(1) is true, and if k in N, P(k) is true, then P(k+2) is true. Is P(n) true for ALL n in N? Why?

Thanks in advace guys!

-William
 
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The principal of induction sezs that if its true for N, it's true for N+1, and we begin with a basis of 1 or zero, usually. This means once we have proved it true for 5, we can deduce that it is true for 6, and if true for 6, well...

So if its true for N+2 when its true for N...you can take it from there.
 
I would say no. P(1) -> P(3) -> P(5) and so on. In other words, P(n) is true for all odd n.
 
Interesting e(hoOn3... I was thinking something like that, other opinions?
 
No. The answer is no.

Well, depending on how N was constructed. You could construct N differently and then be able to say yes.
 
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If you say no, why no? N = Natural numbers,

thanks for your reply!
 
just construct a counter example. it is trivial. P(1), and hence P(3), P(5),.. are true, but P(2) etc can be completely arbitrary. Are you telling me you can't think of an obvious statement that is true for (something to do with) odd numbers but is false for even numbers?
 
Glad there is edit here... its late, I am not thinking straight.
I didnt catch the counter example, sorry.
 
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I am not following you at all.

Matt Grime pretty much gave you a counter example.
 
  • #10
Wrong. Matt didn't give a counter-example per say. He said that one may construct a statement P(n) that is true for odd n but false for even n.
 
  • #11
I think I pretty much did give a counter example. At least if you take second to think what the words ODD and EVEN are doing there. Isn't there a really obvious property that ODD numbers have that EVEN ones don't? And can you show it by induction? Yes. It is a vacuous proof, but still a proof by induction nonetheless.
 
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