Berikelashvilia, Givi, and Nodar Khomeriki. “On the Convergence Rate of a Difference Solution of the Poisson Equation With Fully Nonlocal Constraints”. Nonlinear Analysis: Modelling and Control, vol. 19, no. 3, Oct. 2014, pp. 367-81, https://doi.org/10.15388/NA.2014.3.4.