The answer is, our initial constraint would touch this guy over here. The van to the second motion touches these things over here. The second to third, these guys, and then the landmark observation over here. Put something between x0 and the landmark, that sits here, here, here, here again and here. This observation over here put something between x2 in the landmark. These guys over here, and the guys over here. That means we have only the following places that are still zero. This means there is no direct constraint between x2 and x0. There is this no direct motion information between these guys, and there’s no direct constraint x1 and L, which is this guy is missing over here.