David J. Winter "Normal field extensions ${K \mathord{\left/ {\vphantom {K k}} \right. \kern-\nulldelimiterspace} k}$ and ${K \mathord{\left/ {\vphantom {K k}} \right. \kern-\nulldelimiterspace} k}$ -bialgebras," Bulletin of the American Mathematical Society, Bull. Amer. Math. Soc. 80(3), 506-512, (May 1974)