2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/95581Recently a suggestion has been made that standard textbook representations of hypersurfaces of simultaneity for the travelling twin in the twin "paradox" are incorrect. This suggestion is false: the standard textbooks are in agreement with a proper understanding of the relativity of simultaneity.LaTeX, 3 pages, 2 figures. Update: added new section V and updated referencesClassical Physicstext