An ordinal type defines an ordered set of values in which each value except the first has a unique predecessor and each value except the last has a unique successor.

• 序数类型定义了一个有序的值的集合，集合中的每个值（除第一个）都有一个唯一的前驱值，每个值（除最后一个）都有一个唯一的后继值。