 One can be considerably more precise about the relation between orderings on M and ‘remainder inclusion orderings’ in 𝔘M. Much of this was worked out in Hessenberg (1906), and was therefore known to Zermelo (Zermelo and Hessenberg were in regular contact), and simplified greatly by Kuratowski in the 1920s. We will have reason to refer to Kuratowski briefly in the next section.[30] 