Bellman Equation for Optimal Stopping Time Problems Suzanne Lenhart Indiana University Mathematics Journal 1983 text pdf 10.1512/iumj.1983.32.32026 10.1512/iumj.1983.32.32026 en Indiana Univ. Math. J. 32 (1983) 363 - 375 state-of-the-art mathematics http://iumj.org/access/