Within the quark parton model the two-component duality idea is generalized to single hadron inclusive distributions in deep-inelastic scattering. The discussion is limited to the current fragmentation region. The number of independent distribution functions is reduced. Relations as well as inequalities among the structure functions are obtained. In particular, the excess of π+ over π- in the electroproduction off a proton comes out as a consequence and the differential cross section for e+e- → π+ anything is fully determined by the electroproduction of pions on nucleons.