(defun consolidate (ss)
  (labels ((comb (cs s)
             (cond ((null s) cs)
                   ((null cs) (list s))
                   ((null (intersection s (first cs)))
                    (cons (first cs) (comb (rest cs) s)))
                   ((consolidate (cons (union s (first cs)) (rest cs)))))))
    (reduce #'comb ss :initial-value nil)))