> what mathematicians call "obvious" My favorite joke about this: a math professor starts the class by writing an equation on the board. Then he tells the clas

> what mathematicians call "obvious" My favorite joke about this: a math professor starts the class by writing an equation on the board. Then he tells the class: "from this, it is obvious that--" and writes a second equation below the first. Then the professor stops, wrinkles his forehead, and mutters, "Wait a minute, I may be wrong...". He thinks a few moments more, and then starts writing more equations. More and more equations. Equations covering the whole board. He does this for the rest of the class, and then just before the bell rings, he says "Aha! I was right after all! It is obvious that the second equation follows from the first."