GARDING, Lars. On the asymptotic distribution of the eigenvalues and eigenfunctions of elliptic differential operators. Mathematica Scandinavica, Berkeley, CA, United States, v. 1, p. 237–255, 1953. DOI: 10.7146/math.scand.a-10382. Disponível em: https://journals.msp.org/mscand/article/view/2941. Acesso em: 26 aug. 2026.