Structure of hadron structure functions

We investigate the comparison of the shapes, as functions of $x$, of nonsinglet structure functions of pions and nucleons, $F_{\pi ,N}(x, Q^2)$. We argue that we can predict (to leading twist, all orders of quantum-chromodynamic perturbation theory) the shape of a pion structure function in terms of the observed shape of the nucleon structure function at the same $Q^2$. The uncertainties due to our ignorance of the details of bound-state dynamics are at the 20% level. Our technology is to exploit in detail the relationship between two approaches to the description of structure functions: the operator-product expansion and the covariant parton model.