CHUNG, L. O.; SARIO, L.; WANG, C. Harmonic and polyharmonic degeneracy. MATHEMATICA SCANDINAVICA, [S. l.], v. 40, p. 288–292, 1977. DOI: 10.7146/math.scand.a-11695. Disponível em: https://www.mscand.dk/article/view/11695. Acesso em: 3 may. 2024.