@article{CMH_1979__54_139809,
     author = {Rene Ruchti},
     title = {Twisted {Hopf} {Algebras.}},
     journal = {Commentarii mathematici Helvetici},
     pages = {659--682},
     publisher = {mathdoc},
     volume = {54},
     year = {1979},
     zbl = {0422.16004},
     url = {http://geodesic.mathdoc.fr/item/CMH_1979__54_139809/}
}