[1]  Iwaniec T, Sbordone C. Weak minima of variational integrals. J Reine Angew Math, 1994, 454: 143--161

[2]  高红亚, 王岷, 赵洪亮. A -调和方程障碍问题的很弱解. 数学研究与评论, 2004, 24(1): 159--167

[3]  Meyers N G, Elcrat A. Some results on regularity for solutions of nonlinear elliptic systems and quasi-regular functions. Duke Math J, 1975, 42: 121--136

[4]  Stredulinsky E W. Higher integrability from reverse Hölder inequalities. Indiana Univ Math J, 1980, 29: 408--413

[5]  Li G B, Martio O. Local and global integrability of gradients in obstacle problems. Ann Acad Sci Fenn Ser A I Math, 1994, 19: 25--34

[6]  Lewis J L. On very weak solutions to certain elliptic systems. Comm Part Diff Eqns, 1993, 18: 1515--1537

[7]  Li J, Gao H Y. Local regularity result for very weak solutions of obstacle problems. Radovi Mat, 2003, 12: 19--26

[8]  Giaquinta M, Giusti E. On the regularity of the minima of variational integrals. Acta Math, 1982, 148: 31--46

[9]  Giachetti D, Porzio M M. Local regularity results for minima of functionals of the calculus of variation. Nonlinear
Analysis T M A, 2000, 39: 463--482

[10]  Giaquinta M. Multiple Integrals in the Calculus of Variations and Nonlinear Elliptic Systems. Princeton:  Princeton Univ Press, 1983

[11]  Iwaniec T, Migliaccio L, Nania L, Sbordone C. Integrability results for quasiregular mappings in high dimensions. Math Scand, 1994, 75: 263--279

[12]  Gao H Y, Guo J, Zuo Y L, Chu Y M. Local regularity result in obstacle problem. Acta Math Sci (to appear)