On the Singularities of the Viscosity Solutions to Hamilton-Jacobi-Bellman Equations P. CannarsaH. Soner Indiana University Mathematics Journal 1987 text pdf 10.1512/iumj.1987.36.36028 10.1512/iumj.1987.36.36028 en Indiana Univ. Math. J. 36 (1987) 501 - 524 state-of-the-art mathematics http://iumj.org/access/