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)

83-06 Proceedings, conferences, collections, etc.

83A99 None of the above, but in this section

83Bxx Observational and experimental questions

83B05 Observational and experimental questions

83B99 None of the above, but in this section

83C05 Einstein's equations (general structure, canonical formalism, Cauchy problems)

83C20 Classes of solutions; algebraically special solutions, metrics with symmetries

83C25 Approximation procedures, weak fields

83C27 Lattice gravity, Regge calculus and other discrete methods

83C30 Asymptotic procedures (radiation, news functions, $\scr H$-spaces, etc.)

83C40 Gravitational energy and conservation laws; groups of motions

83C45 Quantization of the gravitational field

83C47 Methods of quantum field theory [See also <a href="#code:81T20">81T20</a>]

83C55 Macroscopic interaction of the gravitational field with matter (hydrodynamics, etc.)

83C60 Spinor and twistor methods; Newman-Penrose formalism

83C65 Methods of noncommutative geometry [See also <a href="#code:58B34">58B34</a>]

83C75 Space-time singularities, cosmic censorship, etc.

83C99 None of the above, but in this section

83Dxx Relativistic gravitational theories other than Einstein's, including asymmetric field theories

83D05 Relativistic gravitational theories other than Einstein's, including asymmetric field theories

83D99 None of the above, but in this section

83Exx Unified, higher-dimensional and super field theories

83E15 Kaluza-Klein and other higher-dimensional theories

83E30 String and superstring theories [See also <a href="#code:81T30">81T30</a>]

83E99 None of the above, but in this section

83F99 None of the above, but in this section