2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/159770This paper is a revised version of a previously posted paper in arxiv. The authors posted it as a new submission by mistake. The latest version of the paper can be found at arXiv:math-ph/0512003v2This paper is a revised version of a previously posted paper in arxiv. The authors posted it as a new submission by mistake. The latest version of the paper can be found at arXiv:math-ph/0512003v2Mathematical PhysicsDifferential Geometrytext