heisenberg's rule of multiplication left me no peace, and after a week of intensive thought and trial, i suddenly remembered an algebraic theory...such quadratic arrays are quite familiar to mathematicians and are called matrices, in association with a definite rule of multiplication. i applied this rule to heisenberg's quantum condition and found that it agreed for the diagonal elements. it was easy to guess what the remaining elements must be, namely, null; and immediately there stood before me the strange formula