On the Kinematic Formula of Square of Mean Curvature Vector Chang-Pao Chen Indiana University Mathematics Journal 1973 text pdf 10.1512/iumj.1973.22.22096 10.1512/iumj.1973.22.22096 en Indiana Univ. Math. J. 22 (1973) 1163 - 1169 state-of-the-art mathematics http://iumj.org/access/