@article{10_4153_CJM_1996_001_8,
     author = {Andruskiewitsch, Nicol\'as and Witsch, Ruskie},
     title = {Notes on {Extensions} of {Hopf} {Algebras}},
     journal = {Canadian journal of mathematics},
     pages = {3--42},
     year = {1996},
     volume = {48},
     number = {1},
     doi = {10.4153/CJM-1996-001-8},
     url = {http://geodesic.mathdoc.fr/articles/10.4153/CJM-1996-001-8/}
}