Product Integral Formulae for Nonlinear Expansive Semi-Groups and Non-Expansive Evolution Systems J. Neuberger Indiana University Mathematics Journal 1970 text pdf 10.1512/iumj.1970.19.19037 10.1512/iumj.1970.19.19037 en Indiana Univ. Math. J. 19 (1970) 403 - 409 state-of-the-art mathematics http://iumj.org/access/