1. L.-E. Andersson, Quasistatic frictional contact problem with finitely many degrees of freedom, LiTH-MAT-R-1999-22, Department of Mathematics (Linköping University, Sweden, 1999).
2. B. Dacorogna, Direct methods in the calculus of variations. In: Applied Mathematical Sciences 78(2), XII+619 (Springer, New York, 2008).
3. On the thermal aspect of dynamic contact problems