@article{CMH_1975__50_139605,
     author = {John N. Mather},
     title = {Commutators of {Diffeomorphisms:} {II.}},
     journal = {Commentarii mathematici Helvetici},
     pages = {33--40},
     publisher = {mathdoc},
     volume = {50},
     year = {1975},
     zbl = {0299.58008},
     url = {http://geodesic.mathdoc.fr/item/CMH_1975__50_139605/}
}