[1] D. Arias and M. Ladra, Central extensions of precrossed modules, Appl. Categ. Structures 12(4) (2004), 339–354.
[2] D. Arias and M. Ladra, Baer invariants and cohomology of precrossed modules, Appl. Categ. Structures 22(1) (2014), 289–304.
[3] M. Barr, ``Exact Categories'', Lecture Notes in Math. 236, Springer, Berlin, 1971, 1-120.
[4] F. Borceux and D. Bourn, ``Mal'cev, Protomodular, Homological and Semi-Abelian Categories'', Mathematics and its Applications, Kluwer, 2004.
[5] F. Borceux and G. Janelidze, ``Galois Theories'', Cambridge Stud. Adv. Math. 72, Cambridge University Press, 2001.
[6] D. Bourn, Normalization equivalence, kernel equivalence and affine categories, Lecture Notes in Math. 1488 (1991), 43-62.
[7] D. Bourn, Mal’cev categories and fibration of pointed objects, Appl. Categ. Structures 4 (1996), 307-327.
[8] D. Bourn, Commutator theory in regular Mal’tsev categories, Fields Inst. Commun. 43 (2004), 61-75.
[9] D. Bourn, Fibration of points and congruence modularity, Algebra Universalis 52(4) (2004), 403-429.
[10] D. Bourn, Internal profunctors and commutator theory; applications to extensions classification and categorical Galois theory, Theory Appl. Categ. 24(17) (2010), 451–488.
[11] D. Bourn and M. Gran, Central extensions in semi-abelian categories, J. Pure Appl. Algebra 175(1-3) (2002), 31-44.
[12] D. Bourn, D and M. Gran, Centrality and normality in protomodular categories, Theory Appl. Categ. 9(8) (2002), 151–165.
[13] D. Bourn and M. Gran, Centrality and connectors in Maltsev categories, Algebra Universalis 48(3) (2002), 309-331.
[14] D. Bourn and M. Gran, Categorical aspects of modularity, Fields Inst. Commun. 43 (2004), 77-100.
[15] D. Bourn and A. Montoli, Intrinsic Schreier-Mac Lane extension theorem II: The case of action accessible categories, J. Pure Appl. Algebra 216(8-9) (2012), 1757–1767.
[16] D. Bourn and D. Rodelo, Comprehensive factorization and I-central extensions, J. Pure Appl. Algebra 216(3) (2012), 598–617.
[17] R. Brown and G. Janelidze, Van Kampen theorems for categories of covering morphisms in lextensive categories, J. Pure Appl. Algebra 119(3) (1997), 255-263.
[18] R. Brown and G. Janelidze, Galois theory of second order covering maps of simplicial sets, J. Pure Appl. Algebra 135(1) (1999), 23-31.
[19] R. Brown and G. Janelidze, Galois theory and a new homotopy double groupoid of a map of spaces, Appl. Categ. Structures 12 (2004), 63-80.
[20] M. Bunge and S. Lack, Van Kampen theorems for toposes, Adv. Math. 179(2) (2003), 291-317.
[21] A. Carboni, Categories of affine spaces, J. Pure Appl. Algebra 61(3) (1989), 243-250.
[22] A. Carboni and G. Janelidze, Decidable (=separable) objects and morphisms in lextensive categories, J. Pure Appl. Algebra 110(3) (1996), 219-240.
[23] A. Carboni and G. Janelidze, Boolean Galois theories, Georgian Math. J. 9(4) (2002), 645-658 (Also preprint Dept. Math. Instituto Superior Téchnico, Lisbon 15, 2002).
[24] A. Carboni, G. Janelidze, G.M. Kelly, and R. Paré, On localization and stabilization of factorization systems, Appl. Categ. Structures 5 (1997), 1-58.
[25] A. Carboni, G. Janelidze, and A.R. Magid, A note on Galois correspondence for commutative rings, J. Algebra 183 (1996), 266-272.
[26] A. Carboni, G.M. Kelly, and M.C. Pedicchio, Some remarks on Maltsev and Goursat categories, Appl. Categ. Structures 1(4) (1993), 385-421.
[27] A. Carboni, J. Lambek, and M.C. Pedicchio, Diagram chasing in Mal’cev categories, J. Pure Appl. Algebra 69(3) (1990), 271-284.
[28] A. Carboni, M.C. Pedicchio, and N. Pirovano, Internal graphs and internal groupoids in Mal’cev categories, CT1991 Proceedings, Canadian Math. Soc. Conf. Proc. 13 (1992), 97-109.
[29] J.M. Casas, E. Khmaladze, M. Ladra, and T. Van der Linden, Homology and central extensions of Leibniz and Lie n-algebras, Homology Homotopy Appl. 13(1) (2011), 59–74.
[30] J.M. Casas and T. Van der Linden, Universal central extensions in semi-abelian categories, Appl. Categ. Structures 22(1) (2014), 253–268.
[31] D. Chikhladze, Monotone-light factorization for Kan fibrations of simplicial sets with respect to groupoids, Homology Homotopy Appl. 6(1) (2004), 501–505.
[32] C. Cassidy, M. Hébert, and G.M. Kelly, Reflective subcategories, localizations, and factorization systems, J. Aust. Math. Soc. (Series A) 38 (1985), 287-329.
[33] D. Chikhladze, Separable morphisms of simplicial sets, J. Homotopy Relat. Struct. 1(1) (2006), 169–173.
[34] M.M. Clementino, A note on the categorical van Kampen theorem, Topology Appl. 158(7) (2011), 926–929.
[35] M.M. Clementino and D. Hofmann, Descent morphisms and a Van Kampen in categories of lax algebras, Topology Appl. 159(9) (2012), 2310–2319.
[36] M.M. Clementino, D. Hofmann, and A. Montoli, Covering morphisms in categories of relational algebras, Appl. Categ. Structures 22(5-6) (2014), 767–788.
[37] M. Duckerts-Antoine, ``Fundamental groups in E-semi-abelian categories'', PhD Thesis, Université catholique de Louvain, Louvain-la-Neuve, 2013.
[38] M. Duckerts, T. Everaert, and M. Gran, A description of the fundamental group in terms of commutators and closure operators, J. Pure Appl. Algebra 216(8-9) (2012), 1837–1851.
[39] M. Duckerts-Antoine, Fundamental group functors in descent-exact homological categories, to appear (and available electronically as http://www.mat.uc.pt/preprints/ps/p1538.pdf).
[40] S. Eilenberg and S. Mac Lane, Natural isomorphisms in group theory, Proc. Natl. Acad. Sci. 28(12) (1942), 537-543.
[41] S. Eilenberg and S. Mac Lane, General theory of natural equivalences, Trans. Amer. Math. Soc. 58(2) (1945), 231-294.
[42] V. Even, A Galois-theoretic approach to the covering theory of quandles, Appl. Categ. Structures 22(5-6) (2014), 817–831.
[43] V. Even and M. Gran, On factorization systems for surjective quandle homomorphisms, J. Knot Theory Ramifications 23(11) (2014), 1450060 (15 pages).
[44] V. Even and M. Gran, Closure operators in the category of quandles, Topology Appl. 200(1) (2016), 237-250.
[45] V. Even, M. Gran, and A. Montoli, A characterization of central extensions in the variety of quandles, to appear in Theory Appl. Categ. 31(8) (2016), 201-216.
[46] T. Everaert, ``An approach to non-abelian homology based on Categorical Galois Theory'', PhD Thesis, Free University of Brussels, Brussels, 2007.
[47] T. Everaert, Higher central extensions and Hopf formulae, J. Algebra 324(8) (2010), 1771–1789.
[48] T. Everaert, Higher central extensions in Mal'tsev categories, Appl. Categ. Structures 22(5-6) (2014), 961–979.
[49] T. Everaert, J. Goedecke, and T. Van der Linden, Resolutions, higher extensions and the relative Mal'tsev axiom, J. Algebra 371 (2012), 132–155.
[50] T. Everaert, J. Goedecke, and T. Van der Linden, The fundamental group functor as a Kan extension, Cah. Topol. Géom. Différ. Catég. 54(3) (2013), 185–210.
[51] T. Everaert and M. Gran, Precrossed modules and Galois theory, J. Algebra 297(1) (2006), 292–309.
[52] T. Everaert and M. Gran, On low-dimensional homology in categories, Homology Homotopy Appl. 9(1) (2007), 275–293.
[53] T. Everaert and M. Gran, Homology of n-fold groupoids, Theory Appl. Categ. 23(2) (2010), 22–41.
[54] T. Everaert and M. Gran, Monotone-light factorisation systems and torsion theories, Bull. Sci. Math. 137(8) (2013), 996-1006.
[55] T. Everaert and M. Gran, Protoadditive functors, derived torsion theories and homology, J. Pure Appl. Algebra 219(8) (2015), 3629–3676.
[56] T. Everaert, M. Gran, and T. Van der Linden, Higher Hopf formulae for homology via Galois theory, Adv. Math. 217 (2008), 2231-2267.
[57] T. Everaert and T. Van der Linden, Baer invariants in semi-abelian categories I: General theory, Theory Appl. Categ. 12(1) (2004), 1-33.
[58] T. Everaert and T. Van der Linden, A note on double central extensions in exact Mal'tsev categories, Cah. Topol. G'{e}om. Diff'{e}r. Cat'{e}g. LI 2 (2010), 143–153.
[59] T. Everaert and T. Van der Linden, Galois theory and commutators, Algebra Universalis 65(2) (2011), 161–177.
[60] T. Everaert and T. Van der Linden, Relative commutator theory in semi-abelian categories, J. Pure Appl. Algebra 216(8-9) (2012), 1791–1806.
[61] T.H. Fay, On commuting congruences in regular categories, Math. Colloq., University of Cape Town 11 (1977), 13-31.
[62] T.H. Fay, On categorical conditions for congruences to commute, Algebra Universalis 8 (1978), 173-179.
[63] R. Freese and R. McKenzie, Commutator theory for congruence modular varieties, London Math. Soc. Lecture Note Ser. 125, Cambridge University Press, 1987.
[64] A. Fr"{o}hlich, Baer-invariants of algebras, Trans. Amer. Math. Soc. 109 (1963), 221-244.
[65] J. Funk and B. Steinberg, The universal covering of an inverse semigroup, Appl. Categ. Structures 18(2) (2010), 135–163.
[66] J. Furtado-Coelho, ``Varieties of $Gamma$-groups and associated functors'', PhD Thesis, University of London, 1972.
[67] J. Furtado-Coelho, Homology and generalized Baer invariants, J. Algebra 40 (1976), 596-609.
[68] J. Goedecke and T. Van der Linden, On satellites in semi-abelian categories: Homology without projectives, Math. Proc. Cambridge Philos. Soc. 147(3) (2009), 629-657.
[69] M. Gran, ``Central extensions of internal groupoids in Maltsev categories'', PhD Thesis, Université Catholique de Louvain, Louvain-la-Neuve, 1999.
[70] M. Gran, Central extensions and internal groupoids in Maltsev categories, J. Pure Appl. Algebra 155(2-3) (2001), 139–166.
[71] M. Gran, Commutators and central extensions in universal algebra, J. Pure Appl. Algebra 174(3) (2002), 249–261.
[72] M. Gran, Applications of categorical Galois theory in universal algebra, Fields Inst. Commun. 43 (2004), 243-280.
[73] M. Gran, ``Structures galoisiennes dans les catégories algébriques et homologiques'', Habilitation à Diriger des Recherches, Université du Littoral Côte d'Opale, 2007.
[74] M. Gran and G. Janelidze, Covering morphisms and normal extensions in Galois structures associated with torsion theories, Cah. Topol. Géom. Différ. Catég. 50(3) (2009), 171-188.
[75] M. Gran and S. Lack, Semi-localizations of semi-abelian categories, J. Algebra 454 (2016), 206-232.
[76] M. Gran and D. Rodelo, Some remarks on pullbacks in Gumm categories, Textos Mat. 46 (2014), University of Coimbra, 125-136 (Also available as arXiv:1408.1342v1 [math.CT] 6 Aug 2014).
[77] M. Gran and V. Rossi, Galois theory and double central extensions, Homology Homotopy Appl. 6(1) (2004), 283–298.
[78] M. Gran and V. Rossi, Torsion theories and Galois coverings of topological groups, J. Pure Appl. Algebra 208(1) (2007), 135-151.
[79] M. Gran and T. Van der Linden, On the second cohomology group in semi-abelian categories, J. Pure Appl. Algebra 212(3) (2008), 636-651.
[80] M. Grandis and G. Janelidze, Galois theory of simplicial complexes, Topology Appl. 132(3) (2003), 281-289.
[81] J.R.A. Gray and T. Van der Linden, Tim Peri-abelian categories and the universal central extension condition, J. Pure Appl. Algebra 219(7) (2015), 2506–2520.
[82] A. Grothendieck, Revêtements étales et groupe fondamental, SGA 1, exposé V, Lecture Notes in Math. 224, Springer, 1971.
[83] H.P. Gumm, An easy way to the commutator in modular varieties, Arch. Math. 34(3) (1980), 220-228.
[84] H.P. Gumm, ``Geometrical methods in congruence modular algebra'', Mem. Amer. Math. Soc. 286, 1983, 79 pages.
[85] J. Hagemann and C. Hermann, A concrete ideal multiplication for algebraic systems and its relationship to congruence distributivity, Arch. Math. 32 (1979), 234-245.
[86] T. Heindel and P. Sobociński, Being van Kampen is a universal property, Log. Methods Comput. Sci. 7(1) (2011), 22 pages.
[87] P.J. Higgins, Groups with multiple operators, Proc. London Math. Soc. 3(6) (1956), 366-416.
[88] G. Janelidze, Magid's theorem in categories, Bull. Georgian Acad. Sci. 114(3) (1984), 497-500 (in Russian).
[89] G. Janelidze, Abelian extensions (of invertible rank, with normal basis) of commutative rings with an infinite number of idempotents, Proc. Math. Inst. Georgian Acad. Sci. LXXVII (1985), 36-49 (in Russian).
[90] G. Janelidze, The fundamental theorem of Galois theory, Math. USSR Sbornik 64(2) (1989), 359-384.
[91] G. Janelidze, Galois theory in categories: the new example of differential fields, Proceedings of the Conference on Categorical Topology, Prague 1988, World Scientific 1989, 369-380.
[92] G. Janelidze, Pure Galois theory in categories, J. Algebra 132 (1990), 270-286.
[93] G. Janelidze, Internal categories in Mal’tsev varieties, York University Preprint, Toronto, 1990.
[94] G. Janelidze, What is a double central extension? (the question was asked by Ronald Brown), Cah. Topol. Géom. Différ. Catég. XXXII-3 (1991), 191-202.
[95] G. Janelidze, Precategories and Galois theory, Lecture Notes in Math. 1488 (1991), 157-173.
[96] G. Janelidze, A note on Barr-Diaconescu covering theory, Contemp. Math. 131(3) (1992), 121-124.
[97] G. Janelidze, Internal crossed modules, Georgian Math. J. 10(1) (2003), 99-114.
[98] G. Janelidze, Categorical Galois theory: revision and some recent developments, Galois Connections and Applications, Kluwer Academic Publishers B.V., 2004, 139-171.
[99] G. Janelidze, Galois groups, abstract commutators, and Hopf formula, Appl. Categ. Structures 16(6) (2008), 653-761.
[100] G. Janelidze, Light morphisms of generalized T0-reflections, Topology Appl. 156(12) (2009), 2109-2115.
[101] G. Janelidze and G.M. Kelly, Galois theory and a general notion of a central extension, J. Pure Appl. Algebra 97(2) (1994), 135-161.
[102] G. Janelidze and G.M. Kelly, The reflectiveness of covering morphisms in algebra and geometry, Theory Appl. Categ. 3 (1997), 132-159.
[103] G. Janelidze and G.M. Kelly, Central extensions in universal algebra: a unification of three notions, Algebra Universalis 44 (2000), 123-128.
[104] G. Janelidze and G.M. Kelly, Central extensions in Mal’tsev varieties, Theory Appl. Categ. 7(10) (2000), 219-226.
[105] G. Janelidze, L. Márki, and W. Tholen, Locally semisimple coverings, J. Pure Appl. Algebra 128(3) (1998), 281-289.
[106] G. Janelidze, L. Márki, and W. Tholen, Semi-abelian categories, J. Pure Appl. Algebra 168(2-3) (2002), 367-386.
[107] G. Janelidze and M.C. Pedicchio, Internal categories and groupoids in congruence modular varieties, J. Algebra 193 (1997), 552-570.
[108] G. Janelidze and M.C. Pedicchio, Pseudogroupoids and commutators, Theory Appl. Categ. 8(15) (2001), 408-456.
[109] G. Janelidze, D. Schumacher, and R.H. Street, Galois theory in variable categories, Appl. Categ. Structures
1(1) (1993), 103-110.
[110] G. Janelidze and R.H. Street, Galois theory in symmetric monoidal categories, J. Algebra 220 (1999), 174-187.
[111] G. Janelidze and W. Tholen, Functorial factorization, well-pointedness and separability, J. Pure Appl. Algebra 142(2) (1999), 99-130.
[112] G. Janelidze and W. Tholen, Extended Galois theory and dissonant morphisms, J. Pure Appl. Algebra 143(1-3) (1999), 231-253.
[113] [JT2010] G. Janelidze and W. Tholen, Strongly separable morphisms in general categories, Theory Appl. Categ. 23(5) (2010), 136-149.
[114] Z. Janelidze, Categorical terms for the shifting lemma, to appear.
[115] T. Janelidze-Gray, Composites of central extensions form a relative semi-abelian category, Appl. Categ. Structures 22(5-6) (2014), 857-872.
[116] M. Jibladze and T. Pirashvili, Linear extensions and nilpotence of Maltsev theories, Beitr. Algebra Geom. 46(1) (2005), 71–102.
[117] P.T. Johnstone, Affine categories and naturally Mal’tsev categories, J. Pure Appl. Algebra 61(3) (1989), 251-256.
[118] E.W. Kiss, Three remarks on the modular commutator, Algebra Universalis 29(4) (1992), 455-476
[119] A. Kock, Generalized fibre bundles, Lecture Notes in Math. 1348 (1988), Springer, 194-207.
[120] A. S.-T. Lue, Baer-invariants and extensions relative to a variety, Proc. Cambridge Philos. Soc. 63 (1967), 569-578.
[121] A. S.-T. Lue, Cohomology of groups relative to a variety, J. Algebra 69 (1981), 155-174.
[122] S. Mac Lane, Groups, categories, and duality, Proc. Natl. Acad. Sci. U.S.A. 47 (1948), 263–267.
[123] S. Mac Lane, Duality for groups, Bull. Amer. Math. Soc. 56 (1950), 485-516.
[124] S. Mac Lane, Categorical algebra, Bull. Amer. Math. Soc. 71 (1965), 40-106.
[125] S. Mac Lane, ``Categories for the Working Mathematician'', Springer, 1971; 2nd Edition 1998.
[126] A.R. Magid, ``The separable Galois theory of commutative rings'', Marcel Dekker, 1974.
[127] A.R. Magid, The separable Galois theory of commutative rings, 2nd Edition, Pure Appl. Math. (Boca Raton), CRC Press, Boca Raton, FL, 2014.
[128] J. Meisen, ``Relations in categories'', PhD Thesis, McGill University, Montreal, 1972.
[129] J. Meisen, Relations in regular categories, Lecture Notes in Math. 418 (1974), Springer, 96-102.
[130] A. Montoli, D. Rodelo, and T. Van der Linden, A Galois theory for monoids, Theory Appl. Categ. 29(7) (2014), 198–214.
[131] M.C. Pedicchio, Maltsev categories and Maltsev operations, J. Pure Appl. Algebra 98(1) (1995), 67-71.
[132] M.C. Pedicchio, A categorical approach to commutator theory, J. Algebra 177 (1995), 647-657.
[133] M.C. Pedicchio, Arithmetical categories and commutator theory, Appl. Categ. Structures 4(2-3) (1996), 297-305.
[134] M.C. Pedicchio, Some remarks on internal pregroupoids in varieties, Comm. Algebra 26(6) (1998), 1737-1744.
[135] G. Peschke, Universal extensions, Comptes Rendus Math. Acad. Sci., Paris 349 (9-10) (2011), 501–504.
[136] D. Rodelo and T. Van der Linden, The third cohomology group classifies double central extensions, Theory Appl. Categ. 23(8) (2010), 150–169.
[137] D. Rodelo and T. Van der Linden, Higher central extensions via commutators, Theory Appl. Categ. 27 (2012), 189–209.
[138] D. Rodelo and T. Van der Linden, Higher central extensions and cohomology, Adv. Math. 287 (2016), 31–108.
[139] V. Rossi, Admissible Galois structures and coverings in regular Mal'{c}ev categories, Appl. Categ. Structures 14(4) (2006), 291–311.
[140] V. Rossi, ``Galois structures and coverings in universal and topological algebra'', PhD Thesis, Udine, 2006.
[141] J.D.H. Smith, ``Mal’cev Varieties'', Lecture Notes in Math. 554, Springer, 1976.
[142] A. Szendrei, ``Commutators and compatible operations'', First Thomasina Coverly Memorial Workshop on Ordered Sets and Universal Algebra, Vanderbilt University, Nashville, TN, USA, May 24-27, 2000.
[143] J.J. Xarez, The monotone-light factorization for categories via preorders, Fields Inst. Commun. 43 (2004), 533-541.
[144] J.J. Xarez, Separable morphisms of categories via preordered sets, Fields Inst. Commun. 43 (2004), 543-549.
[145] J.J. Xarez, Internal monotone-light factorization for categories via preorders, Theory Appl. Categ. 13(15) (2004), 235–251.
[146] J.J. Xarez, A Galois theory with stable units for simplicial sets, Theory Appl. Categ. 15(7) (2005/6), 178–193.
[147] J.J. Xarez, Well-behaved epireflections for Kan extensions, Appl. Categ. Structures 18(2) (2010), 219–230.
[148] J.J. Xarez, Concordant and monotone morphisms, Appl. Categ. Structures 21(4) (2013), 393–415.
[149] I.A. Xarez and J.J. Xarez, Galois theories of commutative semigroups via semilattices, Theory Appl. Categ. 28(33) (2013), 1153–1169.