Negation and Non-Monotonic Reasoning

(:neq  term1 term2)
Succeeds iff NOT term1 = term2. :neq is equivalent to (:lisp (not (eql 'term1 'term2))).

(:fail  form )

(:unp  form )
Unprovable. Succeeds exactly when a query of its path (i.e., form ) fails. :unp is used primarily in default rules. For example:

(:rules Birds
 ((flies ?x True) <- (:unp (not (flies ?x True)))
                     (:assume (normal ?x Birds flies))))

(:assume is discussed below). :unp is a non-monotonic form and to use it successfully you will probably have to understand something of the internals of how Algernon does inference (see section 2.3).

(:assume  predicate)
Adds predicate to the knowledge-base as an assumption. Assumptions differ from facts in two ways. First, an attempt is made to prove the negation of the predicate, and if this attempt succeeds, the :assume fails. Second, any future conclusion which depends on the assumption is tagged with the assumption, so that if the assumption is later withdrawn the conclusion is also withdrawn.