Kuhlmann, Marshall & Osiak 2011, p. 8. Kuhlmann, Salma; Marshall, Murray; Osiak, Katarzyna (1 June 2011), "Cyclic 2-structures and spaces of orderings of power series fields in two variables", Journal of Algebra, 335 (1): 36–48, doi:10.1016/j.jalgebra.2011.02.026
Ille, Pierre; Ruet, Paul (April 2008), "Cyclic extensions of order varieties", Electronic Notes in Theoretical Computer Science, 212: 119–132, doi:10.1016/j.entcs.2008.04.057