[[1] E. Becker, Hereditarily Pythagorean Fields and Orderings of Higher Level, Monografías de Matemática, 29, Instituto de Matemática Pura e Aplicada, Rio de Janeiro, 1978.]Search in Google Scholar
[[2] E. Becker, Summen n-ter Potenzen in Körpern, J. Reine Angew. Math. 307/308 (1979), 8–30.10.1515/crll.1979.307-308.8]Search in Google Scholar
[[3] P. Berrizbeitia, Additive properties of multiplicative subgroups of finite index in fields, Proc. Amer. Math. Soc. 112 (1991), 365–369.10.1090/S0002-9939-1991-1057940-7]Search in Google Scholar
[[4] J. Königsmann, Half-ordered fields, PhD thesis, Universität Konstanz, Konstanz, 1993.]Search in Google Scholar
[[5] T.Y. Lam, The theory of ordered fields, in: B.R. McDonald (ed.), Ring Theory and Algebra, III, Lecture Notes in Pure and Appl. Math., 55, Dekker, New York, 1980, pp. 1–152.]Search in Google Scholar
[[6] T.Y. Lam, Introduction to Quadratic Forms over Fields, Graduate Studies in Mathematics, 67, American Mathematical Society, Providence, RI, 2005.10.1090/gsm/067]Search in Google Scholar
[[7] L. Mahé, J. Mináč and T.L. Smith, Additive structure of multiplicative subgroups of fields and Galois theory, Doc. Math. 9 (2004), 301–355.10.4171/dm/169]Search in Google Scholar
[[8] E. Sperner, Die Ordnungsfunktionen einer Geometrie, Math. Ann. 121 (1949), 107–130.10.1007/BF01329620]Search in Google Scholar
[[9] W.C. Waterhouse. Square root as a homomorphism, Amer. Math. Monthly 119 (2012), 235–239.10.4169/amer.math.monthly.119.03.235]Search in Google Scholar