Pedro González-Casanova Christian Gout Approximation near the boundary of a radial quasi-interpolant in polygonal domains. 1445-1454 2004 81 Int. J. Comput. Math. 12 https://doi.org/10.1080/00207160412331291152 db/journals/ijcm/ijcm81.html#Gonzalez-CasanovaG04