English
For any a in A and any integer n, the counit on the product C a · T n is equal to the counit on a; i.e., the counit is invariant under multiplication by monomials T n in the Laurent polynomial ring.
Русский
Для любого a ∈ A и любого целого числа n counit на произведении C(a) · T(n) равен counit на a; то есть counit инвариантен относитn к монономерам T n в кольце Лорана.
LaTeX
$$$\operatorname{counit}_R( C(a) \cdot T(n) ) = \operatorname{counit}_R(a).$$$
Lean4
@[simp]
theorem counit_C_mul_T (a : A) (n : ℤ) : Coalgebra.counit (R := R) (C a * T n) = Coalgebra.counit (R := R) a := by
simp [← single_eq_C_mul_T]