(defun mode (sequence &rest hash-table-options)
  (let ((frequencies (apply #'make-hash-table hash-table-options)))
    (map nil (lambda (element)
               (incf (gethash element frequencies 0)))
         sequence)
    (let ((modes '())
          (hifreq 0 ))
      (maphash (lambda (element frequency)
                 (cond ((> frequency hifreq)
                        (setf hifreq frequency
                              modes  (list element)))
                       ((= frequency hifreq)
                        (push element modes))))
               frequencies)
      (values modes hifreq))))