1. Ayala, M. and Haase, R. [unpublished]: `Group Contractions and Its Consequences upon Representations of Different Spatial Symmetry Groups', available at
2. Cardin, F. and Marigonda, A. [2004]: `Global World Functions', Journal of Geometry and Symmetry in Physics, 2, available at
3. Chinea, F. J. [1988]: `Symmetries in Tetrad Theories', Classical and Quantum Gravity, 5, available at