English
Insertion distributes over union on the left: insert a b (s1 ∪ s2) = insert a b s1 ∪ s2.
Русский
Вставка над объединением слева дистрибутивна: insert a b (s1 ∪ s2) = insert a b s1 ∪ s2.
LaTeX
$$$ \operatorname{insert}(a,b, (s_1 \cup s_2)) = \operatorname{insert}(a,b,s_1) \cup s_2 $$$
Lean4
theorem insert_union {a} {b : β a} {s₁ s₂ : Finmap β} : insert a b (s₁ ∪ s₂) = insert a b s₁ ∪ s₂ :=
induction_on₂ s₁ s₂ fun a₁ a₂ => by simp [AList.insert_union]