Cyclic quartic local extension without a totally ramified complement
ID: cyclic-quartic-local-extension-without-a-totally-ramified-complement
Let , with , and . The extension is unramified quadratic, whereas is totally ramified quadratic over , by the Eisenstein polynomial . Also , so . The Hensel lemma gives with . Put ; then and . Consequently , defines an automorphism whose square fixes and negates . It generates the cyclic Galois group of order four. Its unique quadratic subfield is , which is unramified. A decomposition as an unramified field and a totally ramified field would require a totally ramified quadratic subfield, and therefore cannot exist.
New to topics? Read the docs here!