Metric tensors for homogeneous, isotropic, 5-dimensional pseudo Riemannian models. Anchordoqui, Luis A.; Birman, Graciela S. — 1998 Revista Colombiana de Matemáticas
Relationship between Laplacian operator and D'Alembertian operator. Birman, Graciela S.; Desideri, Garciela M. — 2004 Divulgaciones Matemáticas