Chapter 2 Section 1 Question 22<br>
<br>
Determine whether each of these sets is the power set of a set, where a 
and b are distinct elements.<br>
<br>
a) Ø<br>

This is not a power set.  It is not even notated as a set.<br>
<br>
b) {Ø,{a}}<br>

This is the power set of {a}<br>
<br>
c) {Ø, {a}, {Ø, a}}<br>

This is not a power set.  If {Ø,a} was the original set, because all 
power sets include the original sets, then the element {Ø} would of had 
to been included.  Power sets are always a power of 2.<br>
<br>
d) {Ø, {a}, {b}, {a,b}}<br>

This is a power set.  It has the right number of elements, 2^2, and it 
has all the individual elements, the Ø, and the original.<br>