A Mathematical Foundation for Radiative Transfer Theory R. Preisendorfer Indiana University Mathematics Journal 1957 text pdf 10.1512/iumj.1957.6.56039 10.1512/iumj.1957.6.56039 en Indiana Univ. Math. J. 6 (1957) 685 - 730 state-of-the-art mathematics http://iumj.org/access/