Classification of Surfaces with Totally Geodesic Gauss Image Bin ChenSeiichi Yamaguchi Indiana University Mathematics Journal 1983 text pdf 10.1512/iumj.1983.32.32011 10.1512/iumj.1983.32.32011 en Indiana Univ. Math. J. 32 (1983) 143 - 154 state-of-the-art mathematics http://iumj.org/access/