Embedding orders into central simple algebras
The question of embedding fields into central simple algebras over a number field was the realm of class field theory. The subject of embedding orders contained in the ring of integers of maximal subfields of such an algebra into orders in that algebra is more nuanced. The first such result along those lines is an elegant result of Chevalley [] which says that with the ratio of the number of isomorphism classes of maximal orders in into which the ring of integers of can be embedded (to...