Hi friends. I have some exercises. If you can help me to solve them I will be greatfull.
1. To prove that every subset from a countable set is countable
2. To prove the following senstences:
a. A is denumerable
b. Exists the function f: A--> N injective
c. Exists the function f ´ :N--> A onto
For though notice that for some countable set there exists some mapping such that is bijective. Thus for some subset clearly the restriction given by is an injection....soo