设R为正整数的有序对集合上的一个关系,当且仅当p–s = q–r时,((p,q),(r,s))∈R。关于R,下列哪一项是正确的?
(A)自反和对称
(B)自反但不对称
(C)不自反但对称
(D)既不反身也不对称答案: (C)
解释:
((p, q), (r, s)) ∈ R if and only if p–s = q–r
(p, q) is not related to (p, q)
as p-q is not same as q-p.
The relation is symmetric because if p–s = q–r, then s-q = s-p.
这个问题的测验