English
If hf is Partrec' on m and hg is a Vec from n to m, then the composition f ∘ g is Partrec' on n.
Русский
Если hf — Partrec' на m и hg — Vec от n к m, то композицiя f ∘ g есть Partrec' на n.
LaTeX
$$$$\forall \{n,m,f,g\},\; \mathrm{Nat.Partrec'}(f) \to \mathrm{Vec}(g) \to \mathrm{Nat.Partrec'}(\lambda v. f (g v)).$$$$
Lean4
theorem comp' {n m f g} (hf : @Partrec' m f) (hg : @Vec n m g) : Partrec' fun v => f (g v) :=
(hf.comp _ hg).of_eq fun v => by simp