These procedures are used to get some information about a list,
or to retrieve one or more elements of a list. Return the number
of elements in list lst. Return the last pair in lst, signalling
an error if lst is circular. Return the kth element from list.
Return the "tail" of lst beginning with its kth element. The
first element of the list is considered to be element 0. list-
cdr-refare identical. It may help to think of list-cdr-refas
accessing the kth cdr of the list, or returning the results of
cdring k times down lst.