Regularity for Elasto-Plastic Type Variational Inequalities R. Jensen Indiana University Mathematics Journal 1983 text pdf 10.1512/iumj.1983.32.32030 10.1512/iumj.1983.32.32030 en Indiana Univ. Math. J. 32 (1983) 407 - 423 state-of-the-art mathematics http://iumj.org/access/