Paper 1, Section II, 18H

Galois Theory
Part II, 2011

Let KK be a field.

(i) Let FF and FF^{\prime} be two finite extensions of KK. When the degrees of these two extensions are equal, show that every KK-homomorphism FFF \rightarrow F^{\prime} is an isomorphism. Give an example, with justification, of two finite extensions FF and FF^{\prime} of KK, which have the same degrees but are not isomorphic over KK.

(ii) Let LL be a finite extension of KK. Let FF and FF^{\prime} be two finite extensions of LL. Show that if FF and FF^{\prime} are isomorphic as extensions of LL then they are isomorphic as extensions of KK. Prove or disprove the converse.