例如，若定义 X 为数的集合，并定义关系 x R y 当且仅当 x 严格小于 y，则 R 的自反闭包为关系 R' 满足“ x R' y 当且仅当 x 小于等于 y “。
英语百科
Reflexive closure 自反闭包
In mathematics, the reflexive closure of a binary relation R on a set X is the smallest reflexive relation on X that contains R.
For example, if X is a set of distinct numbers and x R y means "x is less than y", then the reflexive closure of R is the relation "x is less than or equal to y".