Acuña Ortega, Osvaldo On a definition of finite cardinals in an arbitrary topos. (Spanish) Zbl 0653.18003 Rev. Colomb. Mat. 20, No. 3-4, 79-104 (1986). This paper presents a definition of finite cardinal in an arbitrary topos, using extensional relations, which turns out to be equivalent to the usual (i.e. Kuratowski-finite, decidable and linearly ordered objects). It is also shown that the full subcategory of finite cardinals forms a topos with the axiom of choice. Reviewer: M.Bunge MSC: 18B25 Topoi 03E25 Axiom of choice and related propositions 03E10 Ordinal and cardinal numbers Keywords:finite cardinal PDFBibTeX XMLCite \textit{O. Acuña Ortega}, Rev. Colomb. Mat. 20, No. 3--4, 79--104 (1986; Zbl 0653.18003) Full Text: EuDML