Theorem: mem_union_iff (FM2023Exrcise/section05_sets/sheet1.lean)

State before:
X : Type
A B C D : Set X
x y z : X
⊢ x ∈ A ∪ B ↔ x ∈ A ∨ x ∈ B
Tactic:
rfl
State after:
no goals