2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/199909We investigate Type II orientifolds on non-factorizable torus with and without its oribifolding. We explicitly calculate the Ramond-Ramond tadpole from string one-loop amplitudes, and confirm that the consistent number of orientifold planes is directly derived from the Lefschetz fixed point theorem. We furthermore classify orientifolds on non-factorizable Z_N x Z_M orbifolds, and construct new supersymmetric Type IIA orientifold models on them.42 pages, 3 figures, v2: typos corrected, references added, version to appear in Nucl. Phys. BHigh Energy Physics - Theorytext