
3.12 faCtual KnowleDge 71
3.12.4 Predicates
Predicates are special functions that return only Boolean values, either
“True” or “False.” The predicates are special types of functions that return
only Boolean (true/false) values. The function Father (‘Harry’) discussed
in the previous subsection is a string type and returns ‘James.’ The function
Father (‘Harry,’ ‘James’)returns true if ‘James’ is the father of ‘Harry.’ Note
that Father (‘James,’ ‘Harry’) returns false.
3.12.5 Well-Formed Formulas
A well-formed formula (WFF) is a string of symbols that is generated by a
formal language. That is, a string is a member of the ...