Specifically, two non-abelian anyons labeled a and b have a fusion rule given by a × × b = ∑ ∑ c N a b c c , where the formal sum over c goes over all labels of possible anyon types in the system (as well as the trivial label c = 1 denoting no particles), and each N a b c is a nonnegative integer which denotes how many distinct quantum states there are in which a and b fuse into c (This is true in the abelian case as well, except in that case, for each a and b , there is one type of anyon c for which N a b c = 1 and for all other c , N a b c = 0 .) Each anyon type a should also have a conjugate antiparticle a ¯ ¯ among the list of possible anyon types, such that N a a ¯ ¯ 1 ≠ ≠ 0 , i.e. it can annihilate with its antiparticle. The anyon type label does not specify all of the information about the anyon, but the information that it does indicate is topologically invariant under local perturbations.