Barbero G., J.Fernando, Villaseñor, Eduardo J.S. (2010)

Living Reviews in Relativity [electronic only]

Mikovíc, Aleksandar (2006)

SIGMA. Symmetry, Integrability and Geometry: Methods and Applications [electronic only]

Carlip, Steven (2005)

Living Reviews in Relativity [electronic only]

Burgess, Cliff P. (2004)

Living Reviews in Relativity [electronic only]

Booss-Bavnbek, Bernhelm, Esposito, Giampiero, Lesch, Matthias (2007)

SIGMA. Symmetry, Integrability and Geometry: Methods and Applications [electronic only]

Glinka, Lukasz-Andrzej (2007)

SIGMA. Symmetry, Integrability and Geometry: Methods and Applications [electronic only]