2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/189614We propose a phase factor of the worldsheet S-matrix for strings on AdS_5 x S^5 apparently solving Janik's crossing relation.9 pages, v2: revised conclusions about agreement with perturbative string theory; minor changes, v3: resolution to above problems indicated, to appear in Mod. Phys. Lett. AHigh Energy Physics - Theorytext