Further to David Corfield's post: The diagram below appeared in Frege's 1893 _Grundgesetze der Arithmetik_ ([Vol. I, §§130, 172](https://archive.org/stream/bub_gb_LZ5tAAAAMAAJ#page/n270/mode/2up/search/Bild)) and illustrates the construction of a mapping that Frege uses to prove that for any finite concept, the objects falling under it can be well-ordered. Russell, of course, studied the _Grundgesetze_ closely; perhaps he found inspiration in Frege's figure (if not the almost childish arrows). [![Scan from Grundgesetze der Arithmetik][1]][1] [1]: https://i.sstatic.net/Xwvcw.jpg [2]: https://i.sstatic.net/IgSEo.jpg