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We show that strongly protomodular categories (as the category of groups for instance) provide an appropriate framework in which the commutator of two equivalence relations do coincide with the commutator of their associated normal subobjects, whereas it is not the case in any semi-abelian category.
@article{TAC_2004_13_a1, author = {Dominique Bourn}, title = {Commutator theory in strongly protomodular categories}, journal = {Theory and applications of categories}, pages = {27--40}, publisher = {mathdoc}, volume = {13}, year = {2004}, language = {en}, url = {http://geodesic.mathdoc.fr/item/TAC_2004_13_a1/} }
Dominique Bourn. Commutator theory in strongly protomodular categories. Theory and applications of categories, The Carboni Festschrift, Tome 13 (2004), pp. 27-40. http://geodesic.mathdoc.fr/item/TAC_2004_13_a1/