Further Remarks on the Stress-Deformation Relations for Isotropic Materials R. Rivlin Indiana University Mathematics Journal 1955 text pdf 10.1512/iumj.1955.4.54025 10.1512/iumj.1955.4.54025 en Indiana Univ. Math. J. 4 (1955) 681 - 702 state-of-the-art mathematics http://iumj.org/access/