De, Krishnendu, Uday Chand De, and Ljubica S. Velimirovic. “Some Curvature Properties of Perfect Fluid Spacetimes”. Quaestiones Mathematicae 47, no. 4 (June 20, 2024): 751–764. Accessed October 8, 2026. https://www.ajol.info/index.php/qm/article/view/272233.