Chapter 5.1, Problem 16E

a.

To determine

To show:

If $C$ is an infinite set and $C=A\cup B$ then at least one of the sets $A$ or $B$ is infinite.

b.

To determine

To prove:

Suppose, that $A$ is a set and $p$ is an object not in $A$ . If $A\approx A\cup \left\{p\right\}$ , then $A$ is infinite.