My freedom limits your freedom, if i am an arbitrary obstacle to you. But if that were the case, our freedom could not extend beyond our immediate physical capabilities. One can move around the globe in a boat, how? Because other people helps him. If you are a master, it's because they are forced to do so (by wage). If you are free, it is because they are freely extending your freedom, so you do the same for them. Cooperation is libertarian.
