Corcoran's Aristotelian syllogistic as a subsystem of first-order logic

Aristotelian syllogistic has been formalized for some time now by means of a natural deduction system, called D by John Corcoran. In a classical paper, Corcoran proves a completeness theorem for such a system. His proof involves the use of a reduced system, called RD, that is easier to handle and turns out to be equivalent to D. The question remains, however, whether RD is in fact the easiest such system that is equivalent to D. In this paper we answer this question, but raise some more, by embedding system RD in first-order predicate logic.