39-XX	Difference and functional equations
39-00	General reference works (handbooks, dictionaries, bibliographies, etc.)
39-01	Instructional exposition (textbooks, tutorial papers, etc.)
39-02	Research exposition (monographs, survey articles)
39-03	Historical {!must also be assigned at least one classification number from section 01}
39-04	Explicit machine computation and programs (not the theory of computation or programming)
39-06	Proceedings, conferences, collections, etc.
39Axx	Difference equations {For dynamical systems, see 37-XX}
39A05	General
39A10	Difference equations, additive
39A11	Stability and asymptotics of difference equations, oscillatory and periodic solutions, etc.
39A12	Discrete version of topics in analysis
39A13	Difference equations, scaling (q-differences) [See also 33Dxx]
39A20	Multiplicative and other generalized difference equations, e.g. Of Lyness type
39A70	Difference operators [See also 47B39]
39A99	None of the above, but in this section
39Bxx	Functional equations and inequalities [See also 30D05]
39B05	General
39B12	Iteration theory, iterative and composite equations [See also 26A18, 30D05, 37-XX]
39B22	Equations for real functions [See also 26A51, 26B25]
39B32	Equations for complex functions [See also 30D05]
39B42	Matrix and operator equations
39B52	Equations for functions with more general domains and/or ranges
39B55	Orthogonal additivity and other conditional equations
39B62	Functional inequalities, including subadditivity, convexity, etc. [See also 26A51, 26B25, 26Dxx]
39B72	Systems of functional equations and inequalities
39B82	Stability, separation, extension, and realted topics [See also 46A22]
39B99	None of the above, but in this section