static S joinSubList(L<S> l, int i, int j) {
  ret join(subList(l, i, j));
}

static S joinSubList(L<S> l, int i) {
  ret join(subList(l, i));
}

ifclass IntRange
static S joinSubList(L<S> l, IntRange r) {
  ret r == null ? null : joinSubList(l, r.start, r.end);
}
endif