English
Insertion distributes over intersection: inserting a into the intersection s ∩ t equals the intersection of insert a s and insert a t.
Русский
Вставка элемента в пересечение распределяется: insert a (s ∩ t) = insert a s ∩ insert a t.
LaTeX
$$$\operatorname{insert} a (s \cap t) = (\operatorname{insert} a s) \cap (\operatorname{insert} a t)$$$
Lean4
theorem insert_union : insert a s ∪ t = insert a (s ∪ t) := by grind