week14 - Cardinality Part II Original Notes adopted from...

This preview shows pages 1–2. Sign up to view the full content.

Cardinality Part II Original Notes adopted from January 8, 2002 (Week 14) c P. Rosenthal , MAT246Y1, University of Toronto, Department of Mathematics Definition. | S | = | T | if there exists f : S T (one-to-one and onto) Eg . | Even naturals | = | natural | Definition. If | S | = | N | , then S is countably infinite (or denumerable , or enumerable ) and | S | = 0 (aleph nought). [Elements of S can be listed] | Q | = 0 Theorem. Union of countable number of countable sets is countable. [0,1] is uncountable | [0 , 1] | = c , | R | = c Definition. | S | 6 | T | if there exists T 0 T such that | S 1 | = | T 0 | . ie) There exists f : S T such that f is one-to-one (not necessarily onto). Schroeder-Bernstein(Cantor) Theorem If | S | 6 | T | and | T | 6 | S | , then | S | = | T | . Proof : Given f : S 1:1 T , g : T 1:1 S , we want h : S T (one-to-one and onto). For s S , a first ancestor is a t T such that g ( t ) = s . (If s / g ( T ), no first ancestor.) A next ancestor is an s 1 S such that f ( s 1 ) = t (if such exists). A next ancestor is a t 1 T such that g ( t ) = s 1 , etc, for further ancestors.

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}

What students are saying

• As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

Kiran Temple University Fox School of Business ‘17, Course Hero Intern

• I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

Dana University of Pennsylvania ‘17, Course Hero Intern

• The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

Jill Tulane University ‘16, Course Hero Intern