Section Matrix.
Variable (E : {subfield L}) (A : {set gal_of E}).
Let K := fixedField A.

(* Specifications: *)
Lemma gal_matrix :
{w : #|A|.-tuple L | {subset w <= E} /\ 0 \notin w &
[/\ \matrix_(i, j < #|A|) enum_val i (tnth w j) \in unitmx,
directv (\sum_i K * <[tnth w i]>) &
group_set A -> (\sum_i K * <[tnth w i]>)%VS = E] }.