Corollary. Every infinite set contains a proper subset to which it is similar. Proof. Let A be an infinite set and let S = {a, az, ..} be a count- ably infinite subset of A. The function f: A → A-{a;} defined by (an+1 if x = a, (n = 1, 2, ...), if x € A-S %3D f(x) = (x is a bijection. Thus A ~ A-{a,}. |

Advanced Engineering Mathematics
10th Edition
ISBN:9780470458365
Author:Erwin Kreyszig
Publisher:Erwin Kreyszig
Chapter2: Second-order Linear Odes
Section: Chapter Questions
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Show in detail that is a bijection (Corollary's proof)

ove that every infinite set S contains a proper subset similar to S
Clear search
Theorem 1.42. Every infinite set contains a countably infinite subset.
Proof. Let A be an infinite set. Take some element of A and call
it az. The set A-{az} is not empty; denote one of its elements by az.
This process may be continued indefinitely: at the nth stage the set
A-{a1, ..., an-1}
cannot be empty since A is infinite. The set {a,, a„ ..} is a countably
infinite subset of A. ||
Corollary. Every infinite set contains a proper subset to which it is
similar.
Proof. Let A be an infinite set and let S = {a, az, ..} be a count-
ably infinite subset of A. The function f: A → A-{az} defined by
%3D
(an+1 if x = a, (n = 1, 2, ..),
f(x)
if x e A-S
is a bijection. Thus A ~ A-{az}. |
Transcribed Image Text:ove that every infinite set S contains a proper subset similar to S Clear search Theorem 1.42. Every infinite set contains a countably infinite subset. Proof. Let A be an infinite set. Take some element of A and call it az. The set A-{az} is not empty; denote one of its elements by az. This process may be continued indefinitely: at the nth stage the set A-{a1, ..., an-1} cannot be empty since A is infinite. The set {a,, a„ ..} is a countably infinite subset of A. || Corollary. Every infinite set contains a proper subset to which it is similar. Proof. Let A be an infinite set and let S = {a, az, ..} be a count- ably infinite subset of A. The function f: A → A-{az} defined by %3D (an+1 if x = a, (n = 1, 2, ..), f(x) if x e A-S is a bijection. Thus A ~ A-{az}. |
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