English
For c ∈ ℂ and R ≠ 0, the integral ∮ (z−c)^{-1} over the circle with center c and radius R equals 2πi.
Русский
Для c ∈ ℂ и R ≠ 0 интеграл ∮ (z−c)^{-1} по окружности с центром c и радиусом R равен 2πi.
LaTeX
$$$\\oint z in C(c,R), (z-c)^{-1} = 2\\pi i$ (for $R\\neq 0$)$$
Lean4
theorem integral_add {f g : ℂ → E} {c : ℂ} {R : ℝ} (hf : CircleIntegrable f c R) (hg : CircleIntegrable g c R) :
(∮ z in C(c, R), f z + g z) = (∮ z in C(c, R), f z) + (∮ z in C(c, R), g z) := by
simp only [circleIntegral, smul_add, intervalIntegral.integral_add hf.out hg.out]