@article {1988, title = {Variational inequalities for the biharmonic operator with variable obstacles.}, journal = {Ann. Mat. Pura Appl. (4) 153 (1988), 203-227 (1989)}, number = {SISSA;50/87/M}, year = {1988}, publisher = {SISSA Library}, url = {http://hdl.handle.net/1963/531}, author = {Gianni Dal Maso and Gabriella Paderni} }