History of the classification of mathematical subjects I would like to know if there are sources on the history of the classification of mathematical subjects.
Gérard Lang
 A: Here is one such historical overview:
Mathematics in library subject classification systems, by Craig Fraser (2016). (Springer link)

Insofar as library science is concerned, modern classification of
  mathematical subjects occurred within the larger framework of library
  classification, a vast project receiving sustained attention in the
  period from 1870 to 1920. The work of the library cataloguers was
  carried out against the background of a broad nineteenth-century
  interest in the classification of knowledge. We explore different
  views during this period concerning the position of mathematics in the
  overall scheme of knowledge, the scope of mathematics, and the
  internal organization of the different parts of mathematics. We
  examine how mathematical books were classified, from the most general
  level down to the level of particular subject areas in analysis. The
  focus is on the Library of Congress classification system in its
  various iterations from 1905 to the present.

