It is known that the set of powers of two is recognizable by a finite automaton if the notational base used for representing numbers is itself a power of two but is unrecognizable in all other bases. On the other hand, the set of multiples of two is recognizable no matter what the notational base. It is shown that the latter situation is the exception, the former the rule: the only sets recognizable independently of base are those which are ultimately periodic; others, if recognizable at all, are recognizable only in bases which are powers of some fixed positive integer.
There are several commonly occurring situations in which the position of a unit or member of a waiting line is determined by a priority assigned to the unit rather than by its time of arrival in the line. An example is the line formed by messages awaiting transmission over a crowded communication channel in which urgent messages may take precedence over routine ones. With the passage of time a given unit may move forward in the line owing to the servicing of units at the front of the line or may move back owing to the arrival of units holding higher priorities. Though it does not provide a complete description of this process, the average elapsed time between the arrival in the line of a unit of a given priority and its admission to the facility for servicing is useful in evaluating the procedure by which priority assignments are made. Expressions for this quantity are derived for two cases—the single-channel system in which the unit servicing times are arbitrarily distributed (Eq. 3) and the multiple-channel system in which the servicing times are exponentially distributed (Eq. 6). In both cases it is assumed that arrivals occur at random. Operations Research, ISSN 0030-364X, was published as Journal of the Operations Research Society of America from 1952 to 1955 under ISSN 0096-3984.
Lower bound~on the capacity and on the product of capacity and computation time are obtained for machines which recognize the set of squares. The bound on capacity is approached to within a factor of four by a specific machine which carries out a test based on the fact that every non-square is a quadratic non-residue of some rational prime. A machine which carries out a te st based on the standard root-extraction algorithm is substantially Ie ss efficient in this respect. For neither machine is the bound on the capacity-time product closely approached.
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