@article{CMJ_2004_54_1_a22,
     author = {Sahin, R. and Bizim, O. and Cangul, I. N.},
     title = {Commutator subgroups of the extended {Hecke} groups $\bar{H}(\lambda_q)$},
     journal = {Czechoslovak Mathematical Journal},
     pages = {253--259},
     year = {2004},
     volume = {54},
     number = {1},
     mrnumber = {2040237},
     zbl = {1053.11038},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/CMJ_2004_54_1_a22/}
}