Double Negatives

Let's go back to the fourth grade, shall we? Imagine this:

You're sitting in math class, mindlessly doodling on the corner of your notebook paper, when a paper airplane hits you square on the nose. You jump, startled, but refrain from making a noise because you don't want Mrs. Meanie to send you to the hall . . . again. So, instead, you look in front of you to see a boy looking at you from the corner of his eyes. He gives a slight nod - an indication to open his makeshift paper rocket, and you comply. 'What is 67-(-34)?' Of course, you don't want to give him the answer, so you decide to make your own airplane. You write your note, fold the paper, and strategically aim for the boy's head, but your airplane decides to be a little rebel and spiral around the hit the teacher square on the forehead. You sigh, upset that the teacher will send you out again and that the strange little boy won't ever be able to read your note.

'Two negatives equal a positive.'