2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/196855Pure-radiation solutions are found, exploiting the analogy with the Euler- Darboux equation for aligned colliding plane waves and the Euler-Tricomi equation in hydrodynamics of two-dimensional flow. They do not depend on one of the spacelike coordinates and comprise the Hauser solution as a special subcase.revtex, 9 pagesGeneral Relativity and Quantum Cosmologytext