A Characterization of Orders of Finite Lattice Type.
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 [6] 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...
Let R be a complete discrete valuation ring with quotient field K, L/K be a Galois extension with Galois group G and S be the integral closure of R in L. If a is a factor set of G with values in the group of units of S, then (L/K,a) (resp. Λ =(S/R,a)) denotes the crossed product K-algebra (resp. crossed product R -order in A). In this paper hermitian and quadratic forms on Λ -lattices are studied and the existence of at most two irreducible non-singular quadratic Λ -lattices is proved (Theorem 3.5)....