public static boolean closingIn( Point a1, Point a2, Point b1, Point b2 ){
		Point cut = intersection( a1, plus( a1, new Point( a2.y - a1.y, a1.x - a2.x )), b1, b2 );
		
		int cx = b1.x - cut.x;
		int cy = b1.y - cut.y;
		
		int dx = b1.x - b2.x;
		int dy = b1.y - b2.y;
		
		boolean sx = (cx < 0) == (dx < 0);
		boolean sy = (cy < 0) == (dy < 0);
		return sx && sy;
	}