| | 31-00 | General reference works (handbooks, dictionaries, bibliographies, etc.) |
5 | | 31-01 | Instructional exposition (textbooks, tutorial papers, etc.) |
| 1 | | 31-02 | Research exposition (monographs, survey articles) |
| 2 | | 31-03 | Historical (must also be assigned at least one classification number from Section 01) |
| | 31-04 | Explicit machine computation and programs (not the theory of computation or programming) |
| 6 | | 31-06 | Proceedings, conferences, collections, etc. |
| 4 | (+9) | 31Axx | Two-dimensional theory |
| 7 | (+8) | 31Bxx | Higher-dimensional theory |
| 11 | (+10) | 31Cxx | Other generalizations |
| (+3) | 31Dxx | Axiomatic potential theory |
| | 31Exx | Potential theory on metric spaces |