Integration Formulae and Boundary Conditions for the Hyperbolic Equation with Three Independent Variables and Regions Interior to the Cone W. McCulleyE. Titt Indiana University Mathematics Journal 1953 text pdf 10.1512/iumj.1953.2.52022 10.1512/iumj.1953.2.52022 en Indiana Univ. Math. J. 2 (1953) 443 - 484 state-of-the-art mathematics http://iumj.org/access/