open Or in intro
| inl hs => constructor; left; exact hs; left; exact hs
| inr ⟨ht,hu⟩ => constructor; right; exact ht; right; exact hu
case a.mp
α : Sort u_1
β : ?m.20770
γ : ?m.20773
s t u : Set α
x : α
⊢ x ∈ s.union (t.inter u) → x ∈ (s.union t).inter (s.union u)
no goals