 As has been stressed by Petr Hořava, the K-theory classification of D-branes is independent of, and in some ways stronger than, the classification of BPS states.K-theory appears to classify stable D-branes missed by supersymmetry based classifications.For example, D-branes with torsion charges, that is with charges in the order N cyclic group formula_1, attract each other and so can never be BPS.