42-00 General reference works (handbooks, dictionaries, bibliographies, etc.)
42-01 Instructional exposition (textbooks, tutorial papers, etc.)
42-02 Research exposition (monographs, survey articles)
42-03 Historical (must also be assigned at least one classification number from Section 01)
42-04 Explicit machine computation and programs (not the theory of computation or programming)
42-06 Proceedings, conferences, collections, etc.
42Axx Fourier analysis in one variable
42Bxx Fourier analysis in several variables {For automorphic theory, see mainly 11F30}
42Cxx Nontrigonometric Fourier analysis