(defrule rbrother
(person (name ?x) (gender male))
(person (name ?y))
(parent (parentname ?z) (childname ?x))
(parent (parentname ?z) (childname ?y))
=>
(if (<> (str-compare ?x ?y) 0) then
(printout t ?x “ is a brother of ” ?y crlf)
(assert (brother (name1 ?x) (name2 ?y))))
)