Field theory and polynomials Definition
Galois connection between subgroups and subfields
Definition
Let be a field extension, and let be the group of field automorphisms of that fix every element of . Let be the set of subgroups of and let be the set of intermediate fields of , both ordered by inclusion. For , let be the fixed field of . For , let . The Galois connection between subgroups and subfields of is the pair of maps It is an antitone Galois connection: for all and ,
Remarks
Both sides of the equivalence say that every element of fixes every element of , which is the check. From the equivalence, and , and each map reverses inclusions. Example: for over , the group has four elements, and the maps are inverse bijections between its five subgroups and the five intermediate fields. Non-example of a bijection: for over , the group is trivial, because is the only cube root of in the real field . Then the map sends both and to the trivial group, so it is not injective. The maps are inverse bijections when is a finite Galois extension, by the fundamental theorem of Galois theory.
Reading path
To understand this page from the ground up, read these 13 pages in order. The foundations come first.
Show the path as a graph
- no evidence level
- Group concept
- Ring definition
- Commutative ring definition
- Ring homomorphism definition
- Subring definition
- Unit of a ring definition
- Ring isomorphism definition
- Field definition
- Subfield definition
- Fixed field definition
- Field extension definition
- Intermediate field definition
- Galois connection between subgroups and subfields definition
Further reading
About this page
| Tag | FW68FVNKMJ |
|---|---|
| URI | m2://FW68FVNKMJ |
| Kind | definition |
| Writing | W0 stub |
| MSC | 12F10, 06A15 |
| Defines | Galois connection between subgroups and subfields |
| Uses | Field extension, Intermediate field, Fixed field |
| Changed | 2 November 2026 |
Markdown · JSON · Edit on GitHub
What this page needs for W1
- an inventory row: the row of the inventory that the node accounts for (0 of 1)
- a source with a locator (0 of 1)
The writing levels say how complete the text of a page is. They do not measure its truth.
What links here
No page links to this page yet.