2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/183206The decoupling of zero-norm states leads to linear relations among 4-point functions in the high energy limit of string theory. Recently it was shown that the linear relations uniquely determine ratios among 4-point functions at the leading order. The purpose of this paper is to extend the validity of the same approach to the next-to-leading order and higher orders.17 pages, references added, minor modificationHigh Energy Physics - Theorytext