Crossed modules in Cat and a Brown-Spencer theorem for 2-categories
Cahiers de Topologie et Géométrie Différentielle Catégoriques, Tome 26 (1985) no. 4, pp. 381-388. 
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     author = {Porter, Timothy},
     title = {Crossed modules in $Cat$ and a {Brown-Spencer} theorem for $2$-categories},
     journal = {Cahiers de Topologie et G\'eom\'etrie Diff\'erentielle Cat\'egoriques},
     pages = {381--388},
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     volume = {26},
     number = {4},
     year = {1985},
     mrnumber = {816647},
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     language = {en},
     url = {http://archive.numdam.org/item/CTGDC_1985__26_4_381_0/}
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Porter, Timothy. Crossed modules in $Cat$ and a Brown-Spencer theorem for $2$-categories. Cahiers de Topologie et Géométrie Différentielle Catégoriques, Tome 26 (1985) no. 4, pp. 381-388. http://archive.numdam.org/item/CTGDC_1985__26_4_381_0/

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