Choi Seok-jeong (Korean: 최석정; Hanja: 崔錫鼎; 1646–1715) was a Korean politician and mathematician in the Joseon period of Korea. He published the Gusuryak (Korean: 구수략; Hanja: 九數略) in 1700, the first known literature on Latin squares, predating Leonhard Euler by at least 67 years. He also invented the hexagonal tortoise problem. Choi was a member of the Jeonju Choe clan. Source: Wikipedia (en)