##### Which of the following sets are not well defined? Explain.

Which of the following sets are not well defined? Explain.

a. The set of wealthy school teachers

b. The set of great books

c. The set of natural numbers greater than 100

d. The set of subsets of $$\{1,2,3,4,5,6\}$$

e. The set $$\{x \mid x \neq x$$ and $$x \in N\}$$