05-00 General reference works (handbooks, dictionaries, bibliographies, etc.)
05-01 Instructional exposition (textbooks, tutorial papers, etc.)
05-02 Research exposition (monographs, survey articles)
05-03 Historical (must also be assigned at least one classification number from Section 01)
05-04 Explicit machine computation and programs (not the theory of computation or programming)
05-06 Proceedings, conferences, collections, etc.
05Axx Enumerative combinatorics
05Bxx Designs and configurations {For applications of design theory, see 94C30}
05Cxx Graph theory {For applications of graphs, see 68R10, 90C35, 94C15}
05Dxx Extremal combinatorics
05Exx Algebraic combinatorics