Description: Define the transitive class predicate. Not to be confused with a
transitive relation (see cotr ). Definition of Enderton p. 71
extended to arbitrary classes. For alternate definitions, see dftr2 (which is suggestive of the word "transitive"), dftr3 , dftr4 ,
dftr5 , and (when A is a set) unisuc . The term "complete" is
used instead of "transitive" in Definition 3 of Suppes p. 130.
(Contributed by NM, 29-Aug-1993)