During the scene where John Nash is in his office where his pupil comes in, claiming she has solved the problem, he claims that it's incorrect. She beegs to differ and he takes the sheet of paper. From John's point of veiw, the paper is right-side up, the writing clear on the paper. Then it switches to the opposite point of veiw, and before he hands it back to her, you can clearly see that the paper is upside-down. The margin is at the bottom, rather the top.