2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/230667This paper constructs a presentation for the orthogonal groups. The amalgam is contained in that constructed by Ralf Gramlich Hendrik Van Maldeghem and arXiv:0708.1583 but it's shorter.13 pagesGroup TheoryCombinatorics20G40, 51N30, 20E42, 51E24On a Quasi-Phan Theorem for Orthogonal Groupstext