1. N. Aronszajn, T. M. Creese and L. J. Lipkin, Polyharmonic Functions, Clarendon
Press (Oxford, 1983).
2. S. Axler and W. Ramey, Harmonic polynomials and Dirichlet-type problems, Proc.
Amer. Math. Soc., 123 (1995), 3765–3773.
3. S. Axler, P. Bourdon and W. Ramey, Harmonic Function Theory, 2nd ed., Springer-
Verlag (New York, 2001).
4. M. Brelot and G. Choquet, Polynômes harmoniques et polyharmoniques, in: Second
colloque sur les équations aux dérivées partielles, Bruxelles, 1954, Georges
Thone, Masson & Cie, (Lig̀e, Paris, 1955), pp. 45–66.
5. M. D. Buhmann, Radial Basis Functions. Theory and Implementations, Cambridge
University Press (Cambridge, 2003).