83-00 General reference works (handbooks, dictionaries, bibliographies, etc.)
83-01 Instructional exposition (textbooks, tutorial papers, etc.)
83-02 Research exposition (monographs, survey articles)
83-03 Historical (must also be assigned at least one classification number from Section 01)
83-04 Explicit machine computation and programs (not the theory of computation or programming)
83-05 Experimental work
83-06 Proceedings, conferences, collections, etc.
83-08 Computational methods
83A05 Special relativity
83B05 Observational and experimental questions
83Cxx General relativity
83D05 Relativistic gravitational theories other than Einstein's, including asymmetric field theories
83Exx Unified, higher-dimensional and super field theories
83F05 Cosmology