An Elementary, Direct Proof of Partial Regularity for Solutions of Certain Nonlinear Elliptic Systems L. EvansE. Giarrusso Indiana University Mathematics Journal 1985 text pdf 10.1512/iumj.1985.34.34047 10.1512/iumj.1985.34.34047 en Indiana Univ. Math. J. 34 (1985) 857 - 864 state-of-the-art mathematics http://iumj.org/access/