the supertype relation is reflexive
父类关系是自反的？还是别的什么意思？
如果就是这个意思的话是什么意思。。
虚心求解
不是自反关系，而是预序关系。
https://en.wikipedia.org/wiki/Reflexive_relation
if ∀x,y∈S: x~y ⇒ x~x ∧ y~y.
如果x y是 预序关系，则x y都是自反的。
预序关系的例子
Examples of reflexive relations include:
"is equal to" (equality) 相等
"is a subset of" (set inclusion) 子集
"divides" (divisibility) 划分
"is greater than or equal to" 大于等于
"is less than or equal to" 小于等于
非预序关系的例子
Examples of irreflexive relations include:
"is not equal to" 不等
"is coprime to" (for the integers>1, since 1 is coprime to itself) 互质
"is a proper subset of" 真子集
"is greater than" 大于
"is less than" 小于