Hi PF I am reading an old Rovelli paper http://arxiv.org/abs/gr-qc/9603063 Rovelli computes the entropy of a black hole. He says two things. a) A state is described with an equivalence class of s-knots. b) the entropy of a black hole can be computed by counting the number of the intersection of the horizon and the s-knot (an equivalence class) So when he writes : Let i = 1...n label such intersections What is this n? what is this i labelling?