1. V. Barbu, Optimal Control of Variational Inequalities, vol. 100 ofRes. Notes Math. Pitman, Boston (1984).
2. Bergounioux M., Optimal control problems governed by abstract elliptic variational inequalities with state constraints.SIAM J. Control Optim.36(1998) 273–289.
3. Bonnans F. and Tiba D., Pontryagin’s principle in the control of semilinear elliptic variational inequalities.Appl. Math. Optim.23(1991) 299–312.
4. Casas E., de los Reyes J.C., and Tröltzsch F., Sufficient second-order optimality conditions for semilinear control problems with pointwise state constraints.SIAM J. Optim.19(2008) 616–643.
5. Casas E. and Mateos M., Second order optimality conditions for semilinear elliptic control problems with finitely many state constraints.SIAM J. Control Optim.40(2002) 1431–1454.