Perkins, Sarah B. and Peter J. Rowley. "Bad upward elements in infinite Coxeter groups" Advances in Geometry, 4.4 (2005): 497-511. Retrieved 21 May. 2013, from doi:10.1515/advg.2004.4.4.497

Perkins, S. & Rowley, P. (2005). Bad upward elements in infinite Coxeter groups. Advances in Geometry, 4(4), pp. 413-550. Retrieved 21 May. 2013, from doi:10.1515/advg.2004.4.4.497

Perkins, Sarah B. and Peter J. Rowley. 2005. Bad upward elements in infinite Coxeter groups. Advances in Geometry. 4(4): 413-550. Retrieved 21 May. 2013, from doi:10.1515/advg.2004.4.4.497