oantolin

(defun partition (pred list)
  "Split LIST into elements for which PRED returns true and false."
  (let (true false)
    (dolist (elt list)
      (if (funcall pred elt)
          (push elt true)
        (push elt false)))
    (cons (nreverse true) (nreverse false))))

(defun connected-components (vertices adjacentp)