MASAL'TSEV, L. A. On Isometric Immersion of Three-Dimensional Geometries $SL_2$, $Nil$ and $Sol$ into a Four-Dimensional Space of Constant Curvature. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 57, n. 3, p. 421–426, 2005. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/3609. Acesso em: 6 dec. 2025.