Hamilton's Theory and Generalized Solutions of the Hamilton-Jacobi Equation E. ConwayEberhard Hopf Indiana University Mathematics Journal 1964 text pdf 10.1512/iumj.1964.13.13055 10.1512/iumj.1964.13.13055 en Indiana Univ. Math. J. 13 (1964) 939 - 986 state-of-the-art mathematics http://iumj.org/access/