1. [20] V. V. Zhikov, “On Lavrentiev’s phenomenon”, Russian J. Math. Phys. 3:2 (1995), 249–269.
2. [21] V. V. Zhikov, “On some variational problems”, Russian J. Math. Phys. 5:1 (1997), 105–116.
3. [1] K. Atkinson and W. Han, Theoretical numerical analysis, 3rd ed., Texts in Applied Mathematics 39, Springer, 2009.
4. [2] J.-P. Aubin and I. Ekeland, Applied nonlinear analysis, Wiley, New York, 1984.
5. [3] A. Auslender, Optimisation, Masson, Paris, 1976.