  Current all-orders proofs of factorization of hard processes are made by
extracting the leading power behavior of Feynman graphs, i.e., by extracting
asymptotics strictly order-by-order in perturbation theory. The resulting
parton densities and fragmentation functions include non-perturbative effects.
I show how there are missing elements in the proofs; these are related to and
exemplified by string and cluster models of hadronization. The proofs rely on
large rapidity differences between different parts of graphs for the process;
but in reality large rapidity gaps are filled in
