End MatrixDomain.
Arguments det0P {R n A}.
(* Parametricity at the field level (mx_is_scalar, unit and inverse are only *)
(* mapped at this level).                                                    *)
Section MapFieldMatrix.
Variables (aF : fieldType) (rF : comUnitRingType) (f : {rmorphism aF -> rF}).
Local Notation "A ^f" := (map_mx f A) : ring_scope.

Lemma map_unitmx n (A : 'M_n) : (A^f \in unitmx) = (A \in unitmx).