2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/187991Starting with the whole class of type-D vacuum backgrounds with cosmological constant we show that the separated Teukolsky equation for zero rest-mass fields with spin $s=\pm 2$ (gravitational waves), $s=\pm 1$ (electromagnetic waves) and $s=\pm 1/2$ (neutrinos) is an Heun equation in disguise.27 pages, corrected typo in eq. (1)General Relativity and Quantum Cosmologytext