Atribución-NoComercial-SinDerivadas 4.0 InternacionalAnasagasti, I.Cirre Torres, Francisco Javier2024-10-022024-10-022023-03-30I. Anasagasti, F.J. Cirre, Full automorphism groups of large order of compact bordered Klein surfaces, Journal of Algebra, Volume 628, 2023, Pages 163-188, ISSN 0021-8693, https://doi.org/10.1016/j.jalgebra.2023.03.0150021-8693 | eISSN 1090-266Xhttps://doi.org/10.1016/j.jalgebra.2023.03.015https://hdl.handle.net/20.500.14468/23862Let S be a compact bordered Klein surface of algebraic genus g ≥ 2, and Aut(S) its full group of automorphisms, which is known to have order at most 12(g − 1). In this paper we consider groups G of automorphisms of order at least 4(g − 1) acting on such surfaces, and study whether G is the full group Aut(S) or, on the contrary, the action of G extends to a larger group. The extendability of the action depends first on the NEC signature with which G acts and, in some cases, also on whether a monodromy presentation of G admits or not a particular automorphism. For each signature we study which of the three possibilities [Aut(S) : G] = 1, 2 or 3 occur, and show that, whenever a possibility occurs, it occurs for infinitely many values of g. We find infinite families of groups G, explicitly described by generators and relations, which satisfy the corresponding equality.eninfo:eu-repo/semantics/openAccess12 MatemáticasartículoGroups of automorphismsKlein surfacesExtendability of group actions