KAPITANSKI, L.; RODNIANSKI, I.; YAJIMA, K. On the fundamental solution of a perturbed harmonic sscillator. Topological Methods in Nonlinear Analysis, [S. l.], v. 9, n. 1, p. 77–106, 1997. Disponível em: https://apcz.umk.pl/TMNA/article/view/TMNA.1997.005. Acesso em: 22 jul. 2024.