∀ {S X₁ X₂ : Type u} (f : S ⟶ X₁) (g : S ⟶ X₂) [CategoryTheory.Mono f] (a b : X₁ ⊕ X₂),
  Quot.mk (CategoryTheory.Limits.Types.Pushout.Rel f g) a = Quot.mk (CategoryTheory.Limits.Types.Pushout.Rel f g) b ↔
    CategoryTheory.Limits.Types.Pushout.Rel' f g a b