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.[1] Mr. Eisenhart (Princeton) and Mr. Weitzenböck (Laaren) have also demonstrated in part the mathematical foundations of my new theory, before me.[2] 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.[3] 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).[4] 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.[5] 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.[6] The third article is unfortunately out of print, so that I have to send you my only remaining copy (on the unified field theory).[7] 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.[8] 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.