Howard, Paul; Rubin, Jean E. (1998), "Note 121", Consequences of the Axiom of Choice, Mathematical Surveys and Monographs, vol. 59, Providence, Rhode Island: American Mathematical Society, p. 299, doi:10.1090/surv/059, ISBN0-8218-0977-6, MR1637107
Howard, Paul; Rubin, Jean E. (1998), "Note 121", Consequences of the Axiom of Choice, Mathematical Surveys and Monographs, vol. 59, Providence, Rhode Island: American Mathematical Society, p. 299, doi:10.1090/surv/059, ISBN0-8218-0977-6, MR1637107
Hansson, Bengt (1968), "Choice structures and preference relations", Synthese, 18 (4): 443–458, doi:10.1007/BF00484979, JSTOR20114617; see Lemma 3