39-00 General reference works (handbooks, dictionaries, bibliographies, etc.)
39-01 Instructional exposition (textbooks, tutorial papers, etc.)
39-02 Research exposition (monographs, survey articles)
39-03 Historical (must also be assigned at least one classification number from Section 01)
39-04 Explicit machine computation and programs (not the theory of computation or programming)
39-06 Proceedings, conferences, collections, etc.
39Axx Difference equations {For dynamical systems, see 37-XX}
39Bxx Functional equations and inequalities [See also 30D05]