Spectral Properties of Second Order Differential Operators on Two-step Nilpotent Lie Groups. Journal of Partial Differential Equations, [S. l.], v. 13, n. 1, p. 1–10, 2000. Disponível em: https://gsp.tricubic.dev/jpde/article/view/3927. Acesso em: 15 mar. 2026.