(defun graphsearch (initial-state expand-fn goalp-fn lessp-fn result-fn)
  (loop for open = (list initial-state) 
            then (merge 'list (cdr open) (funcall expand-fn (car open) lessp-fn) lessp-fn)
        when (funcall goalp-fn (car open))
        return (funcall result-fn (car open))))