Time-space optimal parallel set operations

The authors present parallel algorithms for the elementary binary set operations that, given an EREW PRAM (exclusive-read, exclusive-write parallel random-access memory) with k processors, operate on two sorted lists of total length n in O(n/k+log n) time and O(k) extra space, and are thus time-space optimal for any fixed value of k⩽n/(log n). Moreover, the methods are completely general in that they are stable (records with identical keys retain their original relative order), they do not modify records (even temporarily) as they execute, and they require no information other than a record´s key