GRUBB, Gerd. Remainder estimates for eigenvalues and kernels of pseudo-differential elliptic systems. Mathematica Scandinavica, Berkeley, CA, United States, v. 43, p. 275–307, 1978. DOI: 10.7146/math.scand.a-11781. Disponível em: https://journals.msp.org/mscand/article/view/1864. Acesso em: 25 jul. 2026.