lowest upper bound
Let be a set with a partial ordering , and let be a subset of . A lowest upper bound, or supremum, of is an upper bound
of with the property that for every upper bound of . The lowest upper bound of , when it exists, is denoted .
A lowest upper bound of , when it exists, is unique.
Greatest lower bound is defined similarly: a greatest lower bound, or infimum, of is a lower bound of with the property that for every lower bound of . The greatest lower bound of , when it exists, is denoted .
If is a finite set, then the supremum of is simply , and the infimum of is equal to .