static <A> A last(L<A> l) {
  return empty(l) ? null : l.get(l.size()-1);
}

static char last(S s) {
  ret empty(s) ? '#' : s.charAt(l(s)-1);
}

static int last(int[] a) {
  ret l(a) != 0 ? a[l(a)-1] : 0;
}

static <A> A last(A[] a) {
  ret l(a) != 0 ? a[l(a)-1] : null;
}

static <A> A last(Iterator<A> it) {
  A a = null;
  while ping (it.hasNext()) a = it.next();
  ret a;
}