Local Isometric Embeddings of Surfaces into Euclidean Four Space H. Jacobowitz Indiana University Mathematics Journal 1972 text pdf 10.1512/iumj.1972.21.21019 10.1512/iumj.1972.21.21019 en Indiana Univ. Math. J. 21 (1972) 249 - 254 state-of-the-art mathematics http://iumj.org/access/