require import Int.

(* -------------------------------------------------------------------- *)
type t.

op idm : t.
op (+) : t -> t -> t.

theory Axioms.
  axiom nosmt addmA: associative Self.(+).
  axiom nosmt addmC: commutative Self.(+).
  axiom nosmt add0m: left_id idm Self.(+).
end Axioms.

(* -------------------------------------------------------------------- *)
lemma addmA: associative Self.(+).
proof. by apply/Axioms.addmA. qed.

lemma addmC: commutative Self.(+).
proof. by apply/Axioms.addmC. qed.

lemma add0m: left_id idm Self.(+).
proof. by apply/Axioms.add0m. qed.

lemma addm0: right_id idm Self.(+).
proof. by move=> x; rewrite addmC add0m. qed.

lemma addmCA: left_commutative Self.(+).
proof. by move=> x y z; rewrite !addmA (addmC x). qed.

lemma addmAC: right_commutative Self.(+).
proof. by move=> x y z; rewrite -!addmA (addmC y). qed.

lemma addmACA: interchange Self.(+) Self.(+).
proof. by move=> x y z t; rewrite -!addmA (addmCA y). qed.

lemma iteropE n x: iterop n Self.(+) x idm = iter n ((+) x) idm.
proof.
  elim/natcase n => [n le0_n|n ge0_n].
  + by rewrite ?(iter0, iterop0).
  + by rewrite iterSr // addm0 iteropS.
qed.