assert (l.getDirection() == getDirection()) &&
assert (l.getDirection() == getDirection() || (l.x1 == l.x2 && l.y1 == l.y2)) &&
    public void append(IntLine l) {	assert (l.getDirection() == getDirection()) &&	    (l.x1 == x2 && l.y1 == y2);	x2 = l.x2;	y2 = l.y2;    }