Joubert's theorem

In polynomial algebra and field theory, Joubert's theorem states that if and are fields, is a field extension">Field (mathematics)">field extension of of degree 6, and the characteristic of is not equal to 2, then is generated over by some element λ in, such that the minimal polynomial of λ has the form =, for some constants in. The theorem is named in honor of Charles Joubert, a French mathematician, lycée professor, and Jesuit priest.
In 1867 Joubert published his theorem in his paper Sur l'équation du sixième degré in tome 64 of Comptes rendus hebdomadaires des séances de l'Académie des sciences. He seems to have made the assumption that the fields involved in the theorem are subfields of the complex field.
Using arithmetic properties of hypersurfaces, Daniel F. Coray gave, in 1987, a proof of Joubert's theorem. In 2006 gave a proof of Joubert's theorem "based on an enhanced version of Joubert’s argument". In 2014 Zinovy Reichstein proved that the condition characteristic ≠ 2 is necessary in general to prove the theorem, but the theorem's conclusion can be proved in the characteristic 2 case with some additional assumptions on and.