From Undecidability.L Require Export Util.L_facts.
From Undecidability.L.Tactics Require Import LTactics GenEncode.

MetaCoq Run (tmGenEncode "unit_enc" unit).
#[export] Hint Resolve unit_enc_correct : Lrewrite.

Lemma size_unit_enc : size(enc tt) = 2.
Proof. cbv[enc registered_unit_enc size unit_enc]. lia. Qed.