code: public static <C extends Comparable<? super C>> int[]
  	sort(final Seq<? extends C> array) {
  		final IndexSorter sorter = array.size() < INSERTION_SORT_THRESHOLD
  			? InsertionSorter.INSTANCE
  			: HeapSorter.INSTANCE;
  
  		return sorter.sort(array, indexes(array.size()));
  	}
docs: Sorting the given {@code array} by changing the given {@code indexes}.
  The order of the original {@code array} stays unchanged.
  
  @param array the array to sort
  @param <C> the element type
  @return the given {@code indexes} which is now "sorted"
  @throws NullPointerException if one of the arguments is {@code null}