A new article by Joseph Howlett at Quanta explains how Georg Cantor plagiarized Richard Dedekind’s work on infinity.

The case that Cantor plagiarized Dedekind had been made earlier by José Ferreirós (University of Seville), and some earlier mathematicians, such as Emmy Noether (a student of Dedekind’s) seemed to be aware that it had happened.

But now, new correspondence discovered by Demian Goos, a German Argentinian mathematician and journalist, provides further evidence for the accusation.

As Howlett explains, Cantor and Dedekind had been writing a lot to each other about the idea of different-sized infinities:

Energized by Dedekind’s progress, Cantor spent the following days plugging away at the remaining question — the real numbers. Could he finally show that, unlike the algebraic numbers, they were a bigger infinity than the whole numbers?

On December 7, 1873, he wrote to Dedekind that he thought he’d finally succeeded: “But if I should be deceiving myself, I should certainly find no more indulgent judge than you.” He laid out his proof. But it was unwieldy, convoluted. Dedekind replied with a way to simplify Cantor’s proof, building a clearer argument without losing any rigor or accuracy. Meanwhile Cantor, before he’d received Dedekind’s letter, sent him a similar idea for how to streamline the proof, though he hadn’t worked out the details the way Dedekind had.

“The letter from Dedekind to Cantor, dated November 30, 1873, that went missing for more than a century. In it, Dedekind provides a proof that the set of algebraic numbers is the same size as the set of whole numbers — a result that Cantor later plagiarized.” From “The Man Who Stole Infinity” by Joseph Howlett.

The proof “had the potential to shake the math world to its core” but publishing it faced obstacles, such as the fact that the editor of the major math journal of the time, Leopold Kronecker, seemed to think that work on infinity was nonsense, and who also disliked Dedekind because, according to Howlett, “Dedekind had beaten Kronecker to a major result.”

So Cantor made two decisions about how to publish the piece. One had to do with how to present and order its contents, which included a proof by Dedekind about algebraic numbers as well as Dedekind’s cleaner version of Cantor’s argument about real numbers. The other decision was “to claim full authorship for himself. He carefully erased every trace of his collaborator’s contribution, including stray uses of terms that anyone in the know would recognize as Dedekind’s.”

The article was published, and in its wake, “Dedekind stopped replying to Cantor. For nearly three years, they didn’t correspond at all.” But apparently after the two started communicating again about infinity, Cantor plagiarized Dedekind again, and again Dedekind stopped writing him.

The full story is here.