On the lambda and phi operators of radiative transfer theoryDOI: info:10.5479/si.00810231.5-11.153v. 5No. 11Smithsonian Institution153–185
Kumar, Shiv S. 1962. "On the lambda and phi operators of radiative transfer theory." Smithsonian Contributions to Astrophysics, 5, (11) 153–185. https://doi.org/10.5479/si.00810231.5-11.153.