# Mathematics Subject Classification

https://en.wikipedia.org/wiki/Mathematics\_Subject\_Classification

Structure

* MSC is a 3 level deep hierarchical scheme
* classification code can have 2, 3 or 5 digits, depending on specificity

Levels

1. The first level code (FLC) is a 2-digit number.
2. The second level code (SLC) is a letter or a dash.
3. The third level code (TLC) is 2-digit number.

For example

* `53-xx`: Differential geometry (or just `53`)
* `53Axx`: Classical differential geometry (or just `53A`)
* `53A45`: Vector and tensor analysis

**First level**

* _64 mathematical disciplines_ are labeled with a unique 2-digit code.
* there are top-level categories for typical areas and for the overlaps
* mathematical physics is well represented taking categories 70-86
* valid MSC classification codes must have at least FLC.

**Second level**

* SLC are a _letter_ or a _dash_.
* 2nd-level is for specific fields of the 1st-level disciplines.
* SLC vary across the disciplines. e.g.:
  * `53` : Differential Geometry's FLC
  * `53A`: Classical Differential Geometry
  * `53B`: Local Differential Geometry
  * `53C`: Global Differential Geometry
  * `53D`: Symplectic Geometry And Contact Geometry

Second level's special subsection

* dash marks the special subsection, always with the same contents:
  * `FLC-00`: General reference works
  * `FLC-01`: Instructional exposition
  * `FLC-02`: Research exposition
  * `FLC-03`: Historical
  * `FLC-04`: Explicit machine computation and programs
  * `FLC-06`: Proceedings, conferences, collections, etc.
* it is not valid to use trailing dash, e.g. "53-", just use `53`

**Third level**

* 3rd-level codes are the most specific subjects
* TLC ending in 99 is "none-of-the-above", "other" placement for every category

## Using the scheme

The AMS recommends that papers submitted to its journals for publication have one primary classification and one or more optional secondary classifications. A typical MSC subject class line on a research paper looks like:\
`MSC Primary 03C90; Secondary 03-02;`
