By W. Weiss

Show description

Read or Download An Introduction to Set Theory PDF

Best pure mathematics books

Finite Mathematics: An Applied Approach, 11th Edition

Now in its 11th version, this article once more lives as much as its attractiveness as a essentially written, finished finite arithmetic booklet. The 11th version of Finite arithmetic builds upon an outstanding starting place through integrating new beneficial properties and strategies that extra increase pupil curiosity and involvement.

Study Guide for Applied Finite Mathematics

Reasonable and suitable purposes from quite a few disciplines support inspire enterprise and social technological know-how scholars taking a finite arithmetic direction. a versatile supplier permits teachers to tailor the publication to their direction

Extra resources for An Introduction to Set Theory

Sample text

Let κ be an infinite cardinal. The formulas |κ| = |κ × {0}| and |κ × {0}| ≤ |κ × κ| imply that κ ≤ |κ × κ|. We now show that |κ × κ| ≤ κ. We use induction and assume that |λ × λ| = λ for each infinite cardinal λ < κ. We define an ordering on κ × κ by:   max {α0 , β0 } < max {α1 , β1 }; α0 , β0 < α1 , β1 iff max {α0 , β0 } = max {α1 , β1 } ∧ α0 < α1 ; or,   max {α0 , β0 } = max {α1 , β1 } ∧ α0 = α1 ∧ β0 < β1 . It is easy to check that < well orders κ × κ. Let θ = type κ × κ, < . It suffices to show that θ ≤ κ.

5. We say a relation R is total on C whenever ∀x ∈ C ∀y ∈ C [ x, y ∈ R ∨ y, x ∈ R ∨ x = y]. 6. We say R is extensional on C whenever ∀x ∈ C ∀y ∈ C [x = y ↔ ∀z ∈ C ( z, x ∈ R ↔ z, y ∈ R)]. 53 54 CHAPTER 6. RELATIONS AND ORDERINGS An example of a relation R on an ordinal is given by the membership relation: x, y ∈ R iff x ∈ y. R satisfies all the above properties. On the other hand, if α ∈ / ω, the reverse relation R given by x, y ∈ R iff y ∈ x is not well founded but nevertheless has all the other properties.

Using the penultimate lemma, let β0 = max {β : ω β ≤ α} and then let m0 = max {m ∈ ω : ω β0 m ≤ α} which must exist since ω β0 m ≤ α for all m ∈ ω would imply that ω β0 +1 ≤ α. 49 By the previous lemma, there is some α0 ∈ ON such that α = ω β0 m0 + α0 where the maximality of m0 ensures that α0 < ω β0 . Now let β1 = max {β : ω β ≤ α0 } so that β1 < β0 . Proceed to get m1 = max {m ∈ ω : ω β1 m ≤ α0 } and α1 < ω β1 such that α0 = ω β1 m1 + α1 . We continue in this manner as long as possible. We must have to stop after a finite number of steps or else β0 > β1 > β2 > .

Download PDF sample

Rated 4.91 of 5 – based on 50 votes