The WHERE conditions of this query specify various predicates that must be sat- isfied by the attributes of four tuples X, Y, Z, T in a sequence. The evaluation of the applicable predicates on these four variables, however, is not delayed un- til all four tuples are read; instead each predicate is evaluated as soon all its variables in the predicate are known—that is, as soon as the predicate becomes fully instantiated. For instance, the predicate Y:amount