D O C U M E N T 5 2 5 M AY 1 9 2 9 4 5 3 525. To Élie Cartan Berlin, 10 May 1929 Dear Colleague, I must indeed admit that the manifolds that I have employed are a special case of those that you had studied previously. Mr. Eisenhart (Princeton) and Mr. Weitzenböck (Laaren) have also demonstrated in part the mathematical foundations of my new theory, before me. The latter published an article in the Sitzungs- berichte of our Academy, 1928 XXVI, which contained a literature list—presumably complete—of the relevant mathematical papers but he too overlooked your work. This now needs to be rectified. But I am somewhat at a loss over how I should go about doing that in such a way that all the justifiable claims will be satisfied. Yesterday, I submitted a summary article about the matter to the Zeitschrift für Physik, in which I treated the subject in some detail, without mentioning any earlier publications (not even my own). I could add a postscript to that article in which the mathematical antecedents of the theory are treated. But I am afraid that in car- rying out such a plan, I would not be able to describe the contributions of all those involved in a satisfactory fashion. Therefore, I would like to make the following suggestion to you: Write up a brief description of this mathematical history that we can attach to my summary article, of course under your own name, but combined into a unified entity with my paper. You would do me a great favor, and we would together provide a good example of how such priority questions can be dealt with in a respectful and sympathetic manner. I didn’t understand your earlier expositions in Paris at all and it was still less clear to me how they might be utilized within a physical theory. Only last year did I notice that it would be quite natural to adjoin the hypothesis of distant parallelism to the Riemannian metric. That this, however, could actually lead to a theory that would correspond to the present physical knowledge of the physical qualities of space, i.e., to usable field equations, which would be almost uniquely determined by the formal fundamentals—that I have realized only in the last few months. I am enclosing my articles on the subject that have appeared thus far in the [pro- ceedings of the] Academy. The second of these, on the approximate field equa- tions, suffers from the defect that the Hamilton function chosen there renders a centrall symmetric field impossible. The third article is unfortunately out of print, so that I have to send you my only remaining copy (on the unified field theory). I would ask that you return that article to me, along with the article by Weitzenböck, of which I also have only the one copy. The important solution to the problem is to be found only in the last article. In asking you to forgive my unintentional plagiarism, and to help me to put the situation in order, taking account of all the contributions, I remain, with best re- gards, your A. Einstein I will send you the proofs of my article as soon as I receive them.