SUBSET-OF-SET ============= syntax: (subset-of-set <set-of type-A> [:EXTRACT-FN <extract-fn>] [:TEST test-fn] [:TYPE <type-identifier>]) ==> <set-of type-x> This function produces a subset of the given set. Warning: type checking may cause an error! example: >(setf *capital-cities* (subset-of-set *cities* :EXTRACT-FN #'(lambda (a-element) (is-frame-of a-element 'capital-city)) :TYPE 'capital-city)) <set-of CAPITAL-CITY (...)> >(map-set *) (Paris Bruessel Berlin)