simp at h
a✝ m✝ : ℕ
h : Nat.boddDiv2 (2 * a✝) = (true, m✝)
⊢ (match hm : Nat.unpair m✝ with
    | (f, g) =>
      let_fun hn' := (_ : 1 ≤ 2 * a✝);
      let_fun this := (_ : m✝ < 2 * a✝);
      let_fun this_1 := (_ : f < 2 * a✝);
      let_fun this := (_ : g < 2 * a✝);
      cons (decode f) (decode g)) =
    nat a✝
no goals