English
SubtypeVal applied to r composed with toSubtype' r equals a canonical prod constructor.
Русский
SubtypeVal от r после toSubtype' r даёт конструктор prod.mk с fst, snd.
LaTeX
$$\operatorname{subtypeVal}(r) \circ \operatorname{toSubtype'}(r) = \lambda i x . \operatorname{prod.mk} i x.1.fst x.1.snd$$
Lean4
theorem subtypeVal_toSubtype' {α : TypeVec n} (r : α ⊗ α ⟹ «repeat» n Prop) :
subtypeVal r ⊚ toSubtype' r = fun i x => prod.mk i x.1.fst x.1.snd :=
by
ext i x
induction i <;> simp only [toSubtype', comp, subtypeVal, prod.mk] at *
simp [*]