GRUBB, G. Remainder estimates for eigenvalues and kernels of pseudo-differential elliptic systems. MATHEMATICA SCANDINAVICA, [S. l.], v. 43, p. 275–307, 1978. DOI: 10.7146/math.scand.a-11781. Disponível em: https://www.mscand.dk/article/view/11781. Acesso em: 3 may. 2024.