2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/147699We prove that for an orthogonal spacetime metric separable in space and time in comoving coordinates, the requirements of perfect fluid and non-singularity single out the unique family of singularity free cosmological models. Further homogeneous models could only be Bianchi I or FLRW while inhomogeneous ones can be with or without a singularity.TeX pages 13, IUCAA-14/94General Relativity and Quantum Cosmologytext