object agency : travel {\fbox{agency}
agency() :- accept( any ), agency(). book(X,Y) :- reachable(X), price(X,Y). price(amsterdam,5). \$...\$ }
object agency : travel {\fbox{agency}
agency() :- accept( any ), agency(). book(X,Y) :- reachable(X), price(X,Y). price(amsterdam,5). \$...\$ }