Reflection Methods in the Elastic-Plastic Torsion Problem Luis CaffarelliAvner FriedmanGianni Pozzi Indiana University Mathematics Journal 1980 text pdf 10.1512/iumj.1980.29.29014 10.1512/iumj.1980.29.29014 en Indiana Univ. Math. J. 29 (1980) 205 - 228 state-of-the-art mathematics http://iumj.org/access/