private void doMergeSort(int lowerIndex, int higherIndex) {
	         
	        if (lowerIndex < higherIndex) {
	            int middle = lowerIndex + (higherIndex - lowerIndex) / 2;
	            doMergeSort(lowerIndex, middle);
	            doMergeSort(middle + 1, higherIndex);
	            mergeParts(lowerIndex, middle, higherIndex);
	        }
	    }