static <A> L<A> newSubListOrSame(L<A> l, int startIndex) {
  ret newSubListOrSame(l, startIndex, l(l));
}

static <A> L<A> newSubListOrSame(L<A> l, int startIndex, int endIndex) {
  if (l == null) null;
  int n = l(l);
  startIndex = max(0, startIndex);
  endIndex = min(n, endIndex);
  if (startIndex >= endIndex) ret ll();
  if (startIndex == 0 && endIndex == n) ret l;
  ret cloneList(l.subList(startIndex, endIndex));
}

ifclass IntRange
static <A> L<A> newSubListOrSame(L<A> l, IntRange r) {
  ret newSubListOrSame(l, r.start, r.end);
}
endif

Began life as a copy of #1002310