Do cosmic strings determine the number of generations?

What distinguishes the generations above the electroweak scale? We propose a model where three families of leptons and the electroweak bosons are assigned to the irreducible representations of the local binary tetrahedral group of order 24, a discrete subgroup of SU (2), and the local discrete symmetry Z₃. The scattering cross sections of leptons off the cosmic strings associated with the elements of the local discrete symmetry distinguish the members of the lepton families. The possible relevance of the cosmic strings to E₈ unification and the families of quarks are discussed.