  We present a factorization formula for valence quark distributions in a
hadron in x-->1 limit. For the example of pion, we arrive at the form of
factorization by analyzing momentum flow in the leading and high-order Feynman
diagrams. The result confirms the well-known 1-x scaling rule to all orders in
perturbation theory, providing the non-perturbative matrix elements for the
infrared-divergence factors. We comment on re-summation of perturbative single
and double logarithms in 1-x.
