public SLList sublist(int start, int end) {
    	if (start == end) {
    		return NIL;
    	} else {
    		return new SLList(nth(start), sublist(start+1,end));
    	}
    }

    public SLList merge(SLList b) {
    	if (b == NIL) {
    		return this;
    	} else if (this == NIL) {
    		return b;
    	} else if ((int)this.item <= (int)b.item) {
    		return new SLList(this.item, this.next.merge(b));
    	} else {
    		return new SLList(b.first(), this.merge(b.rest()));
    	}
    }

    public SLList mergesort() {
    	//System.out.println("61229");

    	int sli = this.length();
    	if (sli <= 1) {
    		return this;
    	}
    	else {
    		int middle = sli/2;
    		SLList left = this.sublist(0, middle);
    		SLList right = this.sublist(middle, sli);
    		left = left.mergesort();
    		right = right.mergesort();
    		return left.merge(right);
    	}
    }