-- Mathlib/MeasureTheory/Integral/CircleIntegral.lean
theorem norm_integral_lt_of_norm_le_const_of_lt {f : ℂ → E} {c : ℂ} {R C : ℝ} (hR : 0 < R)
    (hc : ContinuousOn f (sphere c R)) (hf : ∀ z ∈ sphere c R, ‖f z‖ ≤ C)
    (hlt : ∃ z ∈ sphere c R, ‖f z‖ < C) : ‖∮ z in C(c, R), f z‖ < 2 * π * R * C

Proof state:
case refine_3
E : Type u_1
inst✝¹ : NormedAddCommGroup E
inst✝ : NormedSpace ℂ E
f : ℂ → E
c : ℂ
R C : ℝ
hR : 0 < R
hc : ContinuousOn f (sphere c R)
hf : ∀ z ∈ sphere c R, ‖f z‖ ≤ C
θ₀ : ℝ
hmem : θ₀ ∈ Ioc 0 (2 * π)
hlt : ‖f (circleMap c R θ₀)‖ < C
⊢ R * ‖f (circleMap c R θ₀)‖ < R * C

Tactic:
exact (mul_lt_mul_left hR).2 hlt

Result:
no goals

Proof state:
E : Type u_1
inst✝¹ : NormedAddCommGroup E
inst✝ : NormedSpace ℂ E
f : ℂ → E
c : ℂ
R C : ℝ
hR : 0 < R
hc : ContinuousOn f (sphere c R)
hf : ∀ z ∈ sphere c R, ‖f z‖ ≤ C
hlt : ∃ z ∈ circleMap c R '' Ioc 0 (2 * π), ‖f z‖ < C
⊢ ‖∮ (z : ℂ) in C(c, R), f z‖ < 2 * π * R * C

Tactic:
rcases hlt with ⟨_, ⟨θ₀, hmem, rfl⟩, hlt⟩

Result:
case intro.intro.intro.intro
E : Type u_1
inst✝¹ : NormedAddCommGroup E
inst✝ : NormedSpace ℂ E
f : ℂ → E
c : ℂ
R C : ℝ
hR : 0 < R
hc : ContinuousOn f (sphere c R)
hf : ∀ z ∈ sphere c R, ‖f z‖ ≤ C
θ₀ : ℝ
hmem : θ₀ ∈ Ioc 0 (2 * π)
hlt : ‖f (circleMap c R θ₀)‖ < C
⊢ ‖∮ (z : ℂ) in C(c, R), f z‖ < 2 * π * R * C

Proof state:
E : Type u_1
inst✝¹ : NormedAddCommGroup E
inst✝ : NormedSpace ℂ E
f : ℂ → E
c : ℂ
R C : ℝ
hR : 0 < R
hc : ContinuousOn f (sphere c R)
hf : ∀ z ∈ sphere c R, ‖f z‖ ≤ C
θ₀ : ℝ
hmem : θ₀ ∈ Ioc 0 (2 * π)
hlt : ‖f (circleMap c R θ₀)‖ < C
⊢ ∫ (θ : ℝ) in 0 ..2 * π, R * ‖f (circleMap c R θ)‖ < ∫ (x : ℝ) in 0 ..2 * π, R * C

Tactic:
refine intervalIntegral.integral_lt_integral_of_continuousOn_of_le_of_exists_lt
    Real.two_pi_pos ?_ continuousOn_const (fun θ _ => ?_) ⟨θ₀, Ioc_subset_Icc_self hmem, ?_⟩

Result:
case refine_1
E : Type u_1
inst✝¹ : NormedAddCommGroup E
inst✝ : NormedSpace ℂ E
f : ℂ → E
c : ℂ
R C : ℝ
hR : 0 < R
hc : ContinuousOn f (sphere c R)
hf : ∀ z ∈ sphere c R, ‖f z‖ ≤ C
θ₀ : ℝ
hmem : θ₀ ∈ Ioc 0 (2 * π)
hlt : ‖f (circleMap c R θ₀)‖ < C
⊢ ContinuousOn (fun θ => R * ‖f (circleMap c R θ)‖) (Icc 0 (2 * π))

case refine_2
E : Type u_1
inst✝¹ : NormedAddCommGroup E
inst✝ : NormedSpace ℂ E
f : ℂ → E
c : ℂ
R C : ℝ
hR : 0 < R
hc : ContinuousOn f (sphere c R)
hf : ∀ z ∈ sphere c R, ‖f z‖ ≤ C
θ₀ : ℝ
hmem : θ₀ ∈ Ioc 0 (2 * π)
hlt : ‖f (circleMap c R θ₀)‖ < C
θ : ℝ
x✝ : θ ∈ Ioc 0 (2 * π)
⊢ R * ‖f (circleMap c R θ)‖ ≤ R * C

case refine_3
E : Type u_1
inst✝¹ : NormedAddCommGroup E
inst✝ : NormedSpace ℂ E
f : ℂ → E
c : ℂ
R C : ℝ
hR : 0 < R
hc : ContinuousOn f (sphere c R)
hf : ∀ z ∈ sphere c R, ‖f z‖ ≤ C
θ₀ : ℝ
hmem : θ₀ ∈ Ioc 0 (2 * π)
hlt : ‖f (circleMap c R θ₀)‖ < C
⊢ R * ‖f (circleMap c R θ₀)‖ < R * C

Proof state:
E : Type u_1
inst✝¹ : NormedAddCommGroup E
inst✝ : NormedSpace ℂ E
f : ℂ → E
c : ℂ
R C : ℝ
hR : 0 < R
hc : ContinuousOn f (sphere c R)
hf : ∀ z ∈ sphere c R, ‖f z‖ ≤ C
hlt : ∃ z ∈ sphere c R, ‖f z‖ < C
⊢ ‖∮ (z : ℂ) in C(c, R), f z‖ < 2 * π * R * C

Tactic:
rw [← _root_.abs_of_pos hR, ← image_circleMap_Ioc] at hlt

Result:
E : Type u_1
inst✝¹ : NormedAddCommGroup E
inst✝ : NormedSpace ℂ E
f : ℂ → E
c : ℂ
R C : ℝ
hR : 0 < R
hc : ContinuousOn f (sphere c R)
hf : ∀ z ∈ sphere c R, ‖f z‖ ≤ C
hlt : ∃ z ∈ circleMap c R '' Ioc 0 (2 * π), ‖f z‖ < C
⊢ ‖∮ (z : ℂ) in C(c, R), f z‖ < 2 * π * R * C

Proof state:
case refine_2
E : Type u_1
inst✝¹ : NormedAddCommGroup E
inst✝ : NormedSpace ℂ E
f : ℂ → E
c : ℂ
R C : ℝ
hR : 0 < R
hc : ContinuousOn f (sphere c R)
hf : ∀ z ∈ sphere c R, ‖f z‖ ≤ C
θ₀ : ℝ
hmem : θ₀ ∈ Ioc 0 (2 * π)
hlt : ‖f (circleMap c R θ₀)‖ < C
θ : ℝ
x✝ : θ ∈ Ioc 0 (2 * π)
⊢ R * ‖f (circleMap c R θ)‖ ≤ R * C

Tactic:
exact mul_le_mul_of_nonneg_left (hf _ <| circleMap_mem_sphere _ hR.le _) hR.le

Result:
no goals

Proof state:
case refine_1
E : Type u_1
inst✝¹ : NormedAddCommGroup E
inst✝ : NormedSpace ℂ E
f : ℂ → E
c : ℂ
R C : ℝ
hR : 0 < R
hc : ContinuousOn f (sphere c R)
hf : ∀ z ∈ sphere c R, ‖f z‖ ≤ C
θ₀ : ℝ
hmem : θ₀ ∈ Ioc 0 (2 * π)
hlt : ‖f (circleMap c R θ₀)‖ < C
⊢ ContinuousOn (fun θ => R * ‖f (circleMap c R θ)‖) (Icc 0 (2 * π))

Tactic:
exact continuousOn_const.mul (hc.comp (continuous_circleMap _ _).continuousOn fun θ _ =>
  circleMap_mem_sphere _ hR.le _).norm

Result:
no goals

Proof state:
E : Type u_1
inst✝¹ : NormedAddCommGroup E
inst✝ : NormedSpace ℂ E
f : ℂ → E
c : ℂ
R C : ℝ
hR : 0 < R
hc : ContinuousOn f (sphere c R)
hf : ∀ z ∈ sphere c R, ‖f z‖ ≤ C
θ₀ : ℝ
hmem : θ₀ ∈ Ioc 0 (2 * π)
hlt : ‖f (circleMap c R θ₀)‖ < C
⊢ ∫ (θ : ℝ) in 0 ..2 * π, ‖deriv (circleMap c R) θ • f (circleMap c R θ)‖ < ∫ (x : ℝ) in 0 ..2 * π, R * C

Tactic:
simp only [deriv_circleMap, norm_smul, norm_mul, norm_circleMap_zero, abs_of_pos hR, norm_I,
  mul_one]

Result:
E : Type u_1
inst✝¹ : NormedAddCommGroup E
inst✝ : NormedSpace ℂ E
f : ℂ → E
c : ℂ
R C : ℝ
hR : 0 < R
hc : ContinuousOn f (sphere c R)
hf : ∀ z ∈ sphere c R, ‖f z‖ ≤ C
θ₀ : ℝ
hmem : θ₀ ∈ Ioc 0 (2 * π)
hlt : ‖f (circleMap c R θ₀)‖ < C
⊢ ∫ (θ : ℝ) in 0 ..2 * π, R * ‖f (circleMap c R θ)‖ < ∫ (x : ℝ) in 0 ..2 * π, R * C

Proof state:
E : Type u_1
inst✝¹ : NormedAddCommGroup E
inst✝ : NormedSpace ℂ E
f : ℂ → E
c : ℂ
R C : ℝ
hR : 0 < R
hc : ContinuousOn f (sphere c R)
hf : ∀ z ∈ sphere c R, ‖f z‖ ≤ C
θ₀ : ℝ
hmem : θ₀ ∈ Ioc 0 (2 * π)
hlt : ‖f (circleMap c R θ₀)‖ < C
⊢ ∫ (x : ℝ) in 0 ..2 * π, R * C = 2 * π * R * C

Tactic:
simp [mul_assoc]

Result:
E : Type u_1
inst✝¹ : NormedAddCommGroup E
inst✝ : NormedSpace ℂ E
f : ℂ → E
c : ℂ
R C : ℝ
hR : 0 < R
hc : ContinuousOn f (sphere c R)
hf : ∀ z ∈ sphere c R, ‖f z‖ ≤ C
θ₀ : ℝ
hmem : θ₀ ∈ Ioc 0 (2 * π)
hlt : ‖f (circleMap c R θ₀)‖ < C
⊢ R * (2 * (π * C)) = 2 * (π * (R * C))

Proof state:
E : Type u_1
inst✝¹ : NormedAddCommGroup E
inst✝ : NormedSpace ℂ E
f : ℂ → E
c : ℂ
R C : ℝ
hR : 0 < R
hc : ContinuousOn f (sphere c R)
hf : ∀ z ∈ sphere c R, ‖f z‖ ≤ C
θ₀ : ℝ
hmem : θ₀ ∈ Ioc 0 (2 * π)
hlt : ‖f (circleMap c R θ₀)‖ < C
⊢ R * (2 * (π * C)) = 2 * (π * (R * C))

Tactic:
ring

Result:
no goals