@article{JSFU_2012_5_3_a2,
     author = {Yaroslav A. Kopylov},
     title = {The {Two-Square} {Lemma} and the connecting morphism in a~preabelian category},
     journal = {\v{Z}urnal Sibirskogo federalʹnogo universiteta. Matematika i fizika},
     pages = {316--325},
     publisher = {mathdoc},
     volume = {5},
     number = {3},
     year = {2012},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/JSFU_2012_5_3_a2/}
}