1. Harper's Series in Modern Mathematics;Freyd, Peter,1964
2. Construction de préschémas quotient;Gabriel, Pierre,1963
3. The category of finite bialgebras over a field;Oort, Frans;Nederl. Akad. Wetensch. Proc. Ser. A 70 = Indag. Math.,1967
4. Mathematics Lecture Note Series;Sweedler, Moss E.,1969