The Maslov and Morse indices for Schrodinger operators on R Peter Howard Indiana University Mathematics Journal 2018 text pdf 10.1512/iumj.2018.67.7462 10.1512/iumj.2018.67.7462 en Indiana Univ. Math. J. 67 (2018) 1765 - 1815 state-of-the-art mathematics http://iumj.org/access/