@article{articled98699df,
title   = {On mean value solutions for the Helmholtz equation on square grids},
author = {Val, João Bosco Ribeiro do and Andrade, Marinho Gomes de},
year = {2002},
doi = {10.1016/S0168-9274(01)00127-1},
journal   = {Applied Numerical Mathematics}
}