Question

Finish the following proof for Theorem 1.4.12. Assume B is a countable set. Thus, there exists f : N -+ B, which is 1-1 and onto. Let A ~ B be an infinite subset of B. We must show that A is countable. Let nI = min{n EN: f(n) E A}. As a start to a definition of g: N -+ A, set g(l) = f(nI). Show how to inductively continue this process to produce a 1-1 function 9 from N onto A.

Answer 1

A is a countable set

Explanation:

Assume B is a countable set, Go through the attached file for a detailed step by step explanation of the proof that A is a countable set.