;;;###autoload
(defun sort-on (sequence predicate accessor)
"Sort SEQUENCE by calling PREDICATE on sort keys produced by ACCESSOR.
-SEQUENCE should be the input list or vector to sort.
+SEQUENCE should be the input sequence to sort.
Elements of SEQUENCE are sorted by keys which are obtained by
calling ACCESSOR on each element. ACCESSOR should be a function of
one argument, an element of SEQUENCE, and should return the key