Typo Correction & Hint
Problem #33, page 258

(1) FIRST:
I see that in some copies of the text, there is a misprint of the 
statement of this problem.  The correct version of the problem is:

	For all sets  A,B, and C,

        	(A-B)+(B-C) = (A+B)-(B.C)

The proof boils down  to showing that:

        A-C is a subset of  (A-B) + (B-C)

One way to prove this is to first prove that:

        A-C = [A-(B+C)] + [(A.B)-C]

Then prove that:

        A-(B+C) is a subset of A-B

and that

        (A.B)-C is a subset of B-C

(3) THIRD:
Please note that "+" denotes UNION, and "." denotes INTERSECTION.