English
If each X_i is a TopologicalSpace and T0, then the space ∀ i, X_i is a T0-space.
Русский
Если каждая X_i — топологическое пространство и T0, то пространствo ∀ i X_i является T0.
LaTeX
$$$\text{If } X_i\ (i\in I)\text{ are Topological spaces with } T0, \; \forall i, X_i\text{ is T0.}$$$
Lean4
instance instT0Space {ι : Type*} {X : ι → Type*} [∀ i, TopologicalSpace (X i)] [∀ i, T0Space (X i)] :
T0Space (∀ i, X i) :=
⟨fun _ _ h => funext fun i => (h.map (continuous_apply i)).eq⟩