Grades [On the maximalorder of permutations of given degree], Arch. Math. Phys. Ser. 3, vol. 5, 1903, pp. 92-103. W. Miller, The maximum order of an element
数学分支序理论中,預序集子集 S {\displaystyle S} 的極大元(英語:maximal elements)不小於 S {\displaystyle S} 的任何元素。極小元(minimal elements)可對偶地(英语:Duality (order theory))定義,其不大於 S {\displaystyle