theorem Set.exttheorem Set.ext: ∀ {α : Type u} {a b : Set α}, (∀ (x : α), x ∈ a ↔ x ∈ b) → a = b
Published by @sam · Jul 21, 2026
View source in zpg9xh52
zpg9xh52
Definitional, with no premises to accept.
Set.ext
definitional fact