 Complete the following phrase:  The World Professional Billiards and Snooker Association WPBSA, the governing body for professional snooker, first introduced a ranking system for professional players in 1976, with the aim of seeding players for the World Snooker Championship. The reigning champion would be automatically seeded first, the losing finalist from the previous year seeded second, and the other seedings based on the ranking list. Initially the rankings were based on performances in the preceding three world championships, with five points for the winner, four for the runner-up, three for losing semi-finalists, two for losing quarter-finalists, and on for losers in the last 16 round. Following the 