intro
| ⟨inr hu, _⟩ => right; exact hu
| ⟨_, inr hu⟩ => right; exact hu
| ⟨inl hs, inl ht⟩ => left; constructor; exact hs; exact ht
case a.mpr
α : Sort u_1
β : ?m.21318
γ : ?m.21321
s t u : Set α
x : α
⊢ x ∈ (s.union u).inter (t.union u) → x ∈ (s.inter t).union u
no goals