@article{CMH_1985__60_140003,
     author = {John N. Mather},
     title = {Commutators of diffeomorphisms, {III:} a group which is not perfect.},
     journal = {Commentarii mathematici Helvetici},
     pages = {122--124},
     publisher = {mathdoc},
     volume = {60},
     year = {1985},
     zbl = {0575.58011},
     url = {http://geodesic.mathdoc.fr/item/CMH_1985__60_140003/}
}