# How do you prove induction from well-ordering principle?

## How do you prove induction from well-ordering principle?

Equivalence with Induction First, here is a proof of the well-ordering principle using induction: Let S S S be a subset of the positive integers with no least element. Clearly, 1 ∉ S , 1\notin S, 1∈/​S, since it would be the least element if it were. Let T T T be the complement of S ; S; S; so 1 ∈ T .

### What is proof of induction and why do we prove by induction?

A proof by induction consists of two cases. The first, the base case (or basis), proves the statement for n = 0 without assuming any knowledge of other cases. The second case, the induction step, proves that if the statement holds for any given case n = k, then it must also hold for the next case n = k + 1.

Can you prove anything by induction?

Proofs by Induction A proof by induction is just like an ordinary proof in which every step must be justified. However it employs a neat trick which allows you to prove a statement about an arbitrary number n by first proving it is true when n is 1 and then assuming it is true for n=k and showing it is true for n=k+1.

How do you prove induction examples?

Proof by Induction : Further Examples Prove by induction that 11n − 6 is divisible by 5 for every positive integer n. 11n − 6 is divisible by 5. Base Case: When n = 1 we have 111 − 6=5 which is divisible by 5. So P(1) is correct.

## What is the principle of induction?

The principle of induction is a way of proving that P(n) is true for all integers n ≥ a. It works in two steps: (a) [Base case:] Prove that P(a) is true. (b) [Inductive step:] Assume that P(k) is true for some integer k ≥ a, and use this to prove that P(k + 1) is true.

### How do you prove well-ordered?

The proof is by well ordering. Let C be the set of all integers greater than one that cannot be factored as a product of primes. We assume C is not empty and derive a contradiction. If C is not empty, there is a least element, n 2 C, by well ordering.

How do you prove the natural numbers are well-ordered?

The Well-Ordering Principle can be used to prove all sort of theorems about natural numbers, usually by assuming some set \$T\$ is nonempty, finding a least element \$n\$ of \$T\$, and “inducting backwards” to find an element of \$T\$ less than \$n\$–thus yielding a contradiction and proving that \$T\$ is empty.

Is the well-ordering principle the same as the principle of mathematical induction?

In this sense, the Well-Ordering Principle and the Principle of Mathematical Induction are just two ways of looking at the same thing. Indeed, one can prove that WOP, PCI, and PMI are all logically equivalent, so we could have taken any one of them as our fifth axiom for the natural numbers. Fundamental Theorem of Arithmetic.

## How do you prove that strong induction is true?

Strong Induction Implies WOP We prove this by contradiction, so assume that the well-ordering principle is false. Then there exists some nonempty set S⊆Z+ S ⊆ Z +, which does not have a least element. Now consider the following statement P (n) P ( n) says that n∉S n ∉ S . We will prove that P (n) P ( n) is true for all n∈Z+ n ∈ Z + by induction.

### What is the well-ordering principle?

The well-ordering principle is a property of the positive integers which is equivalent to the statement of the principle of mathematical induction. Every nonempty set b b ’s belonging. Many constructions of the integers take it as an axiom.

What are the principles of induction?

First, we give the statements of the principles. Any nonempty set of positive integers has a least element. For the two forms of induction, let P (n) P ( n) be some proposition depending on n n. For instance, P (n) P ( n) could be the proposition “there are n people in this room”.