Section FrobeniusAutomorphism.
Variables (p : nat) (charRp : p \in [char R]).
Canonical Frobenius_aut_additive := Additive Frobenius_aut_is_rmorphism.
Canonical Frobenius_aut_rmorphism := RMorphism Frobenius_aut_is_rmorphism.
End FrobeniusAutomorphism.

Lemma exprB m n x : n <= m -> x \is a unit -> x ^+ (m - n) = x ^+ m / x ^+ n.