  Supposing only that there is an effective charge which defines an evolution
scheme for parton distribution functions (DFs) that is all-orders exact, strict
lower and upper bounds on all Mellin moments of the valence-quark DFs of
pion-like systems are derived. Exploiting contemporary results from numerical
simulations of lattice-regularised quantum chromodynamics (QCD) that are
consistent with these bounds, parameter-free predictions for pion valence,
glue, and sea DFs are obtained. The form of the valence-quark DF at large
values of the light-front momentum fraction is consistent with predictions
derived using the QCD-prescribed behaviour of the pion wave function.
