ABSTRACT

Time-dependent events a(t) and b(t) are said to commute if the occurrence of a(t) during a time interval T followed by the occurrence of b(t) during an interval S leads to an outcome that does not change when the order of events is reversed. Denoting by b(S)a(T) the occurrence of a followed by b, then a(T)b(S) denotes the reversed order, and a and b commute if a(T)b(S) = b(S)a(T). Otherwise, a and b are said to be noncommutative events.