English
The concatenation of identity arrows on α and on β is the identity on the concatenated object α ::: β; equivalently, (TypeVec.id n α ::: id β) = TypeVec.id.
Русский
Соединение единичных морфизмов на α и на β равно единице на объединённом векторе α ::: β; то есть (TypeVec.id n α ::: id β) = TypeVec.id.
LaTeX
$$$$\\big(\\text{TypeVec.appendFun}(\\text{TypeVec.id}, \\text{id})\\big) = \\text{TypeVec.id}.$$$$
Lean4
theorem appendFun_id_id {α : TypeVec n} {β : Type*} : (@TypeVec.id n α ::: @_root_.id β) = TypeVec.id :=
eq_of_drop_last_eq rfl rfl