"n","m")。例如，2为4的因数及6为72的因数，则可写成2|4和6|72，或"D"(2,4)和"D"(6,72)。
共面.对三维空间内的线"L"，存在一个三条线为共面的三元关系。此一关系「无法」缩减成两条线共面的二元对称关系。换句话说，若 "P"("L","M","N")表示线 "L","M","N"共面，且"Q"("L","M")表示线 "L","M"共面，则"Q"("L","M"),"Q"("M","N")和"Q"("N","L")不能合起来代表"P"("L","