Hypothesis charR2 : 2 \in [char R].

(* Specifications: *)
Lemma addrr_char2 x : x + x = 0. Proof. by rewrite -mulr2n mulrn_char. Qed.
Lemma oppr_char2 x : - x = x.
Lemma subring_closed_semi : subring_closed -> semiring_closed.
End ClosedPredicates.