Actually, Tony was on the right track.

The cancellation operation (where we cancel out the (A-B) factors on each side is actually a division -- we are dividing each side of the equation by (A-B), and since A-B = 0, we are dividing by zero, which is, of course, an illegal operation. Multiplying by zero is allowable, and does not cause any uncomfortable results.

Ain't math fun?

tanstaafl.

"There Ain't No Such Thing As A Free Lunch"