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 unitrE x : (x \is a unit) = (x / x == 1).