ZORN'S LEMMA

noun Etymology: Max August Zorn died 1993 German mathematician Date: circa 1950 a lemma in set theory: if a set S is partially ordered and if each subset for which every pair of elements is related by exactly one of the relationships “less than,” “equal to,” or “greater than” has an upper bound in S, then S contains at least one element for which there is no greater element in S