55-00 General reference works (handbooks, dictionaries, bibliographies, etc.)
55-01 Instructional exposition (textbooks, tutorial papers, etc.)
55-02 Research exposition (monographs, survey articles)
55-03 Historical (must also be assigned at least one classification number from Section 01)
55-04 Explicit machine computation and programs (not the theory of computation or programming)
55-06 Proceedings, conferences, collections, etc.
55Mxx Classical topics {For the topology of Euclidean spaces and manifolds, see 57Nxx}
55Nxx Homology and cohomology theories [See also 57Txx]
55Pxx Homotopy theory {For simple homotopy type, see 57Q10}
55Qxx Homotopy groups
55Rxx Fiber spaces and bundles [See also 18F15, 32Lxx, 46M20, 57R20, 57R22, 57R25]
55Sxx Operations and obstructions
55Txx Spectral sequences [See also 18G40, 55R20]
55Uxx Applied homological algebra and category theory [See also 18Gxx]