## Arthur Cayley to H. Poincaré

Cambridge, 25 June, 1888

Dear Mr. Poincaré,

I received some time ago the scheme for the Répertoire bibliographique des Mathématiques, but am only able to admire the very careful & apparently complete way in which the classification has been made. I do not return the copy as I have not made any notes upon it as yet, and am now unable to do so, as we are just going for a Swiss tour.

The plan seems to me a very beautiful one, if it can be carried out: but there will be serious difficulties, a memoir must in some cases have to be entered under a great many of the different subheadings, and to do this properly would require a careful study of the whole memoir.

Would it be possible to give to each of the subheadings some kind of a historical and explanatory introduction? The nature of this would vary a good deal in the several cases: for instance A1 and A2, hardly anything would be required; and so A5; they are part of one’s general knowledge of Analysis: but A3 and A4 might each of them be, and it would be interesting to do them, in considerable detail. So also in B2, one would be glad to have a definition of the group hypo-abélien, and of the several kinds of group included under $\delta$. But one would see better what is desirable and practicable, if one actually tried to write out such introduction for a few different cases.

Believe me, dear Mons. Poincaré, yours very sincerely.

A. Cayley

ALS 3p. Private collection, Paris 75017.

Time-stamp: " 4.05.2019 01:00"