Double Checking

An experimental physicist had completed an important experiment on the determination of the relationship betwen two physical quantities A and B. He rushed across the campus to the office of a theoretical mathematician who was occupied with the same problem. "Volodya! I have finished the experiment. A has turned out to be larger than B!"

The mathematician thought about this for a moment before replying. "This is completely understandable. You didn't even have to make your experiment, as A must be larger than B for the following reasons..."

"Oh dear," interuppted the physicist. "Did I really say that A was larger than B? I slipped up -- it is B that is larger than A!"

The mathematician thought about this for a moment more before replying. "Then this is even more understandable, and here is why..."