private static void isort(String[] a, String[] aux, int l, int h, int d) {
		// insertion sort
		for (int i = l; i <= h; i++)
			for (int j = i; j > l && less(a[j], a[j - 1], d); j--) {
				// swap a[j - 1], a[j]
				String temp = a[j - 1];
				a[j - 1] = a[j];
				a[j] = temp;
			}
			
	}