English
If φ is existentially quantified, realizing φ is preserved under embeddings; i.e., Realize is compatible with composition with coefficients of morphisms when φ is existential.
Русский
Если φ существует, реализация φ сохраняется под встраиванием; то есть Realize совместима с композициями коэффициентов морфизмов при существовании φ.
LaTeX
$$$\varphi.IsExistential \to (\forall f, \varphi.Realize v xs \Rightarrow \varphi.Realize (f\circ v) (f\circ xs))$$$
Lean4
theorem realize_embedding {φ : L.BoundedFormula α n} (hU : φ.IsUniversal) (f : F) {v : α → M} {xs : Fin n → M} :
φ.Realize (f ∘ v) (f ∘ xs) → φ.Realize v xs := by
induction hU with
| of_isQF hQF => simp [hQF.realize_embedding]
| all _ ih =>
simp only [realize_all, Nat.succ_eq_add_one]
refine fun h a => ih ?_
rw [Fin.comp_snoc]
exact h (f a)