2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/55522We obtain an M--theory interpretation of different IIA orientifold planes by compactifying them on a circle and use a chain of dualities to get a new IIA limit of these objects using this circle as the eleventh dimension. Using the combination of the two IIA description, we give an interpretation for all orientifold four-planes in M-theory, including a mechanism for freezing M5-branes at singularities.16 pages, 4 figures, LaTeXHigh Energy Physics - Theorytext