A Predicate is a sentence-forming Relation.
Each tuple in the Relation is a finite, ordered sequence of objects.
The fact that a particular tuple is an element of a Predicate is denoted
by '(*predicate* arg_1 arg_2 .. arg_n)', where the arg_i are the
objects so related. In the case of BinaryPredicates, the fact can
be read as `arg_1 is *predicate* arg_2' or `a *predicate* of
arg_1 is arg_2'.
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