Many volumes have been published under this title purporting to reveal an infallible method of attaining success in a lottery. La Clef d'or, or La Véritable trésor de la fortune (1810), reprinted from time to time at Lille, Belgium, is based on the doctrine of sympathetic numbers, which the anonymous author claims to have discovered from study of the works of Cagliostro, Cornelius Agrippa, and others. Each number drawn, he declares, has five sympathetic numbers that directly follow it. For example, the number 4 has for its sympathetic numbers 30, 40, 50, 20, and 76. With this knowledge it is claimed to be an easy matter to win a lottery.