A note on double central extensions in exact maltsev categories
Cahiers de Topologie et Géométrie Différentielle Catégoriques, Tome 51 (2010) no. 2, article no. 4, 11 p. 
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     author = {Everaert, Tomas and Van Der Linden, Tim},
     title = {A note on double central extensions in exact maltsev categories},
     journal = {Cahiers de Topologie et G\'eom\'etrie Diff\'erentielle Cat\'egoriques},
     eid = {4},
     pages = {143--153},
     publisher = {Andr\'ee CHARLES EHRESMANN},
     volume = {51},
     number = {2},
     year = {2010},
     mrnumber = {2667981},
     zbl = {1215.18013},
     language = {en},
     url = {http://www.numdam.org/item/CTGDC_2010__51_2_143_0/}
}
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Everaert, Tomas; Van Der Linden, Tim. A note on double central extensions in exact maltsev categories. Cahiers de Topologie et Géométrie Différentielle Catégoriques, Tome 51 (2010) no. 2, article  no. 4, 11 p. http://www.numdam.org/item/CTGDC_2010__51_2_143_0/

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