In mathematics, a cyclically ordered group is a set with both a group structure and a cyclic order, such that left and right multiplication both preserve the cyclic order.
It is natural to depict cyclically ordered groups as quotients: one has Zn = Z/nZ and T = R/Z. Even a once-linear group like Z, when bent into a circle, can be thought of as Z2 / Z. Rieger (1946, 1947, 1948) showed that this picture is a generic phenomenon. For any ordered group L and any central element z that generates a cofinal subgroup Z of L, the quotient group L / Z is a cyclically ordered group. Moreover, every cyclically ordered group can be expressed as such a quotient group.[2]
The circle groupedit
Świerczkowski (1959a) built upon Rieger's results in another direction. Given a cyclically ordered group K and an ordered group L, the product K × L is a cyclically ordered group. In particular, if T is the circle group and L is an ordered group, then any subgroup of T × L is a cyclically ordered group. Moreover, every cyclically ordered group can be expressed as a subgroup of such a product with T.[3]
By analogy with an Archimedean linearly ordered group, one can define an Archimedean cyclically ordered group as a group that does not contain any pair of elements x, y such that [e, xn, y] for every positive integern.[3] Since only positive n are considered, this is a stronger condition than its linear counterpart. For example, Z no longer qualifies, since one has [0, n, −1] for every n.
As a corollary to Świerczkowski's proof, every Archimedean cyclically ordered group is a subgroup of T itself.[3] This result is analogous to Otto Hölder's 1901 theorem that every Archimedean linearly ordered group is a subgroup of R.[4]
Topologyedit
Every compact cyclically ordered group is a subgroup of T.
Related structuresedit
Gluschankof (1993) showed that a certain subcategory of cyclically ordered groups, the "projectable Ic-groups with weak unit", is equivalent to a certain subcategory of MV-algebras, the "projectable MV-algebras".[5]
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Pecinová-Kozáková, Eliška (2005), "Ladislav Svante Rieger and His Algebraic Work", in Safrankova, Jana (ed.), WDS 2005 - Proceedings of Contributed Papers, Part I, Prague: Matfyzpress, pp. 190–197, CiteSeerX10.1.1.90.2398, ISBN 978-80-86732-59-6
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Further readingedit
Černák, Štefan (1989a), "Completion and Cantor extension of cyclically ordered groups", in Hałkowska, Katarzyna; Stawski, Boguslaw (eds.), Universal and Applied Algebra (Turawa, 1988), World Scientific, pp. 13–22, ISBN 978-9971-5-0837-1, MR 1084391
Černák, Štefan (1989b), "Cantor extension of an Abelian cyclically ordered group" (PDF), Mathematica Slovaca, 39 (1): 31–41, hdl:10338.dmlcz/128948, retrieved 21 May 2011
Černák, Štefan (1991), "On the completion of cyclically ordered groups" (PDF), Mathematica Slovaca, 41 (1): 41–49, hdl:10338.dmlcz/131783, retrieved 22 May 2011
Černák, Štefan (1995), "Lexicographic products of cyclically ordered groups" (PDF), Mathematica Slovaca, 45 (1): 29–38, hdl:10338.dmlcz/130473, retrieved 21 May 2011
Černák, Štefan (2001), "Cantor extension of a half linearly cyclically ordered group", Discussiones Mathematicae - General Algebra and Applications, 21 (1): 31–46, doi:10.7151/dmgaa.1025
Černák, Štefan (2002), "Completion of a half linearly cyclically ordered group", Discussiones Mathematicae - General Algebra and Applications, 22 (1): 5–23, doi:10.7151/dmgaa.1043
Černák, Štefan; Jakubík, Ján (1987), "Completion of a cyclically ordered group", Czechoslovak Mathematical Journal, 37 (1): 157–174, doi:10.21136/CMJ.1987.102144, hdl:10338.dmlcz/102144, MR 0875137, Zbl 0624.06021
Fuchs, László (1963), "IV.6. Cyclically ordered groups", Partially ordered algebraic systems, International series of monographs in pure and applied mathematics, vol. 28, Pergamon Press, pp. 61–65, LCC QA171 .F82 1963
Giraudet, M.; Kuhlmann, F.-V.; Leloup, G. (February 2005), "Formal power series with cyclically ordered exponents" (PDF), Archiv der Mathematik, 84 (2): 118–130, CiteSeerX10.1.1.6.5601, doi:10.1007/s00013-004-1145-5, S2CID 16156556, retrieved 30 April 2011
Harminc, Matúš (1988), "Sequential convergences on cyclically ordered groups" (PDF), Mathematica Slovaca, 38 (3): 249–253, hdl:10338.dmlcz/128594, retrieved 21 May 2011
Hölder, O. (1901), "Die Axiome der Quantität und die Lehre vom Mass", Berichte über die Verhandlungen der Königlich Sachsischen Gesellschaft der Wissenschaften zu Leipzig, Mathematische-Physicke Klasse, 53: 1–64
Jakubík, Ján (1989), "Retracts of abelian cyclically ordered groups" (PDF), Archivum Mathematicum, 25 (1): 13–18, hdl:10338.dmlcz/107334, retrieved 21 May 2011
Jakubík, Ján (1990), "Cyclically ordered groups with unique addition", Czechoslovak Mathematical Journal, 40 (3): 534–538, doi:10.21136/CMJ.1990.102406, hdl:10338.dmlcz/102406
Jakubík, Ján (1991), "Completions and closures of cyclically ordered groups" (PDF), Czechoslovak Mathematical Journal, 41 (1): 160–169, doi:10.21136/CMJ.1991.102447, hdl:10338.dmlcz/102447, MR 1087637, retrieved 21 May 2011
Jakubík, Ján (1998), "Lexicographic product decompositions of cyclically ordered groups" (PDF), Czechoslovak Mathematical Journal, 48 (2): 229–241, doi:10.1023/A:1022881202595, hdl:10338.dmlcz/127413, S2CID 55134686, retrieved 21 May 2011
Jakubík, Ján (2008), "Sequential convergences on cyclically ordered groups without Urysohn's axiom", Mathematica Slovaca, 58 (6): 739–754, doi:10.2478/s12175-008-0105-0
Jakubík, Ján; Pringerová, Gabriela (1988), "Representations of cyclically ordered groups" (PDF), Časopis Pro Pěstování Matematiky, 113 (2): 184–196, doi:10.21136/CPM.1988.118342, hdl:10338.dmlcz/118342, retrieved 30 April 2011
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Pecinová, Eliška (2008), Ladislav Svante Rieger (1916–1963), Dějiny matematiky (in Czech), vol. 36, Prague: Matfyzpress, hdl:10338.dmlcz/400757, ISBN 978-80-7378-047-0, retrieved 9 May 2011
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