methods. If a pair of methods op1 and op2 are compatible, the summation of the quorum numbers of op1 and op2 can be smaller than the number of replicas in the QOL protocol even if op1 or op2 change the state of the object. We newly propose a version vector which can be used to identify which methods are performed on a replica. We discuss the QOL protocol, where the replicas exchange the compatible methods performed by themselves but not by others, by means of the version vector.