2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/35166Fock representations are constructed for a free scalar field in the closed and quasi-Euclidean isotropic cosmological models. Invariance of their cyclic vector (vacuum) under isometries and the correspondence principle single out a class of unitarily equivalent representations.7 pages, gc.sty. Published for the first time in Russian in 1968 as JINR Preprint. With E.A. Tagirov's comment of September 2004General Relativity and Quantum Cosmologytext