(defgrammar one-of
((one-of ?word) ?word))
(defgrammar two-of
((two-of ?word) (one-of ?word) (one-of ?word)))
Each of these defines a 3-ary relation, whose extra argument is the word to match. When the relations are called, the word will typically be bound to a symbol from the sentence to match.
The following will succeed and bind ?x to the list (foo bar):
(clog:any '?x '(two-of (start start foo bar) ?x start))
The following will both fail because the sentences do not begin with two start symbols:
(clog:any '?x '(two-of (not-start start foo bar) ?x start))
(clog:any '?x '(two-of (start not-start foo bar) ?x start))
KnowledgeWorks and Prolog User Guide (Unix version) - 24 Mar 2017