The Fifteen Theorem states that if a positive-definite quadratic form defined by a symmetric, integral matrix takes on the values 1, 2, 3, 5, 6, 7, 10, 14, 15, then it takes all positive integer values. The theorem was astonishingly discovered by John Conway and William Schneeberger in 1993, though their complex proof was later simplified by Manjul Bhargava in 2000. Bhargava also developed other universality results, such as showing that a list of 29 integers guarantees a quadratic form takes all positive integer values, even if not defined by a symmetric integral matrix.