Advice in problem solving: “You must always invert.” — Carl Gustav Jacob Jacobi “Whenever you can, count.” — Francis Galton “Each problem that I solved became a rule, which served afterwards to solve other problems.” — Descartes “By studying the masters, not their pupils.” — Niels Henrik Abel “Truth is the offspring of silence and meditation. I keep the subject constantly before me and wait ’til the first dawnings open slowly, by little and little, into a full and clear light.” — Isaac Newton