open Or in intro
| ⟨inl hs, hu⟩ => left; constructor; exact hs; exact hu
| ⟨inr ht, hu⟩ => right; constructor; exact ht; exact hu
case a.mp
α : Sort u_1
β : ?m.22335
γ : ?m.22338
s t u : Set α
x : α
⊢ x ∈ (s.union t).inter u → x ∈ (s.inter u).union (t.inter u)
no goals