* Borceux, F. "Handbook of Categorical Algebra: vol 1 Basic category theory" (1994) Cambridge University Press, (Encyclopedia of Mathematics and its Applications) ISBN 0-521-44178-1* N. Bourbaki, "Livre II : Algèbre" (1970), Hermann, ISBN 0-201-00639-1.
* Borceux, F. "Handbook of Categorical Algebra: vol 1 Basic category theory" (1994) Cambridge University Press, (Encyclopedia of Mathematics and its Applications) ISBN 0-521-44178-1* N. Bourbaki, "Livre II : Algèbre" (1970), Hermann, ISBN 0-201-00639-1.