In recent years there has been renewed interest in the calculus of variations, motivated in part by ongoing research in materials science and other dis- plines. Often, the study of certain material instabilities such as phase tran- tions, formation of defects, the onset of microstructures in ordered materials, fractureanddamage, leadstothesearchforequilibriathroughaminimization problem of the type min{I(v): v?V}, wheretheclassV ofadmissiblefunctionsv isasubsetofsomeBanachspaceV. This is the essence of the calculus of variations: the identi?cation of nec- sary and su?cient conditions on the...