2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/42376I discuss a degree of freedom in formulating perturbation theory that is often neglected: the in- and out-states need not be empty. The inclusion of (free) particles in the asymptotic states modifies the on-shell prescription of the free propagator. This affects loop contributions -- but the modified expansion is {\it a priori} as justified as the standard one with Feynman prescription. It is possible to dress the quark propagator to all orders with zero-momentum gluons from the perturbative ground state. The dressed quark has no pole and thus cannot appear as an external particle in the S-matrix. Chiral symmetry may be spontaneously broken, but Lorentz and gauge symmetry is exact. Adding loop corrections to this ``dressed tree approximation'' gives a formally exact PQCD expansion.Prepared for the Festschrift in honor of Jan Kwiecinski, to be published in Acta Physica Polonica. 8 pages, 2 figures. Uses appolb.clsHigh Energy Physics - Phenomenologytext