This is a Common Mistake
•Suppose you had two sets.  Set S1 is the result of searching for ‘fear’ (4,055 records) and set S2 is ‘math or mathematics’ (58,984 records):
•
•?S 1 AND 2
•          203089  1
•          198285  2
•      S4  169200  1 AND 2
•?
• What has happened here???
We’ve seen this mistake before!  Look at the huge resulting set!  If there are only 58,984 records on math or mathematics, why is set S4 so doggone large?  Using an AND Operator should yield something smaller than the 4,055 record set for fear.  In this case, I’ve asked the computer to look for the “word” “1” instead of using the set “S1”.  The same thing happened with the other set.