Some topics don't seem to fit into just one category of the Mathematics Subject Classification scheme. This page will be a home for them, although right now it's just sort of garbage file. If you know what you're looking for but couldn't find any good matches in the Layman's Guide, try scanning this file for some keywords that seem appropriate for your needs.
There are some areas of mathematics (?) which fall outside the MSC altogether; it's unclear what to offer as a good site for these. For example, one might mention
The sphere FAQ and (division) ring FAQ written some time ago do not seem to fit so neatly into these area boundaries, but we have tried to give them appropriate cross-links as well.
There are some topics which are discussed in several areas of the MSC. We try in such cases to provide crosslinks. See for example the division of material on polynomials, mentioned in the page for 12F: Galois theory.
It looks like there should be multi-heading pages for some parts of mathematics with greatly overlapping resources. For the most part these seem to coincide with the broad-area classifications the AMS used in the MSC until 1972 (see below for defunct MSC codes):
There are many closely allied pairs of fields, too: Probability(60)/Statistics(62), Logic(03)/Set Theory(04), Geometry(51)/Convex Geometry(52), etc.; but pairs of pages are probably easily crosslinked, that is, there's probably no need to set up "parent" pages for these pairs.
There are some subjects which, based on reports in the popular press and the presentations in the undergraduate curriculum, one might expect to be major portions of the subject classification system. Did you look for these in vain? Here are a few pointers:
There are some topics which just aren't mathematics! It's always possible, perhaps, that a person lands at this web site completely by mistake. What non-mathematical query might have brought you here?:
Perhaps it's also appropriate to show the nearest cognates with other classification systems. e.g. Computing Reviews? AIP? See the page for 00-XX. [Computing reviews: http://www.acm.org/class]
One might envision other ways to break up the discipline and see how even they are. Sample topics: distribution of SIAM members' fields of interest; distribution of Fields medalists; division of math fields in AMS's annual list of recent PhDs; etc.
What about the defunct parts of the MSC? A few fields were discarded after a reorganization: 02 (became 03), 10 (became 11), 21 (became 22), 50 (became 51); A few fields were for papers unclassifiable except for broad field: 09(algebra), 27(analysis), 36 (differential equations), 48(geometry), 56(topology), 69(applied math), 99(misc). Some numbers were apparently never used: 7,23-25,29,37-38, 59,61,63-64,66-67,74-75,77,87-89,95-98
For more detail on old classifications, see URL: http://www.ams.org/msnmain?screen=Classification
09 (40-72) Classical algebra
09-XX (40-72) Classical algebra 09.0X (40-58) Algebra 09.00 (59-72) Classical algebra 09.1X (40-58) Abstract algebra 09.2X (40-58) Elementary algebra 09.3X (40-58) Rings, fields and algebras
21 (40-58) Topological algebraic structures
21-XX (40-58) Topological algebraic structures 21.0X (40-58) Topological algebraic structures
27 (40-58) Analysis
27-XX (40-58) Analysis 27.0X (40-58) Analysis 27.1X (40-58) Foundations of analysis 27.2X (40-58) Theory of sets, theory of functions of real variables 27.3X (40-58) Theory of functions of real variables, theory of measure and integration 27.4X (40-58) Geometrical analysis 27.5X (40-58) Functions with particular properties
36 (40-58) Differential equations, operational calculus
36-XX (40-58) Differential equations, operational calculus 36.0X (40-58) Differential equations 36.1X (40-58) Differential equations, operational calculus
48 (40-58) Geometry
48-XX (40-58) Geometry 48.0X (40-58) Geometry
56 (40-58) Topology
56-XX (40-58) Topology 56.0X (40-58) Topology
69 (40-72) General applied mathematics
69-XX (40-72) General applied mathematics 69.00 (59-79) General Applied Mathematics
71 (40-58) Mechanics
71-XX (1940-1958) Mechanics 71.0X (1940-1958) Mechanics
79 (40-58) Mathematical physics, physical applications
79-XX (1940-1958) Mathematical physics, physical applications 79.0X (1940-1958) Mathematical physics, physical applications
84 (40-58) Relativity, astronomy
84-XX (1940-1958) Relativity, astronomy 84.0X (1940-1958) Relativity, astronomy
91 (40-58) Other applications
91-XX (1940-1958) Other applications 91.0X (1940-1958) Other applications
99 (40-58) Miscellaneous
99-XX (40-58) Miscellaneous 99.0X (40-58) Miscellaneous
Like we said, this is still sort of a garbage file...