2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/104462As a homage to A K Raychaudhuri, I derive in a straightforward way his famous equation and also indicate the problems he was last engaged in.8 pages, latex file, Pedagogical, One technical incorrect statement corrected and some minor rephrasingGeneral Relativity and Quantum CosmologyAstrophysicsHigh Energy Physics - Theorytext