-- Mathlib/Analysis/Complex/PhragmenLindelof.lean
theorem right_half_plane_of_bounded_on_real (hd : DiffContOnCl ℂ f {z | 0 < z.re})
    (hexp : ∃ c < (2 : ℝ), ∃ B,
      f =O[cobounded ℂ ⊓ 𝓟 {z | 0 < z.re}] fun z => expR (B * ‖z‖ ^ c))
    (hre : IsBoundedUnder (· ≤ ·) atTop fun x : ℝ => ‖f x‖) (him : ∀ x : ℝ, ‖f (x * I)‖ ≤ C)
    (hz : 0 ≤ z.re) : ‖f z‖ ≤ C

Proof state:
E : Type u_1
inst✝¹ : NormedAddCommGroup E
inst✝ : NormedSpace ℂ E
C : ℝ
f : ℂ → E
z✝ : ℂ
hexp : ∃ c < 2, ∃ B, f =O[cobounded ℂ ⊓ 𝓟 {z | 0 < z.re}] fun z => expR (B * ‖z‖ ^ c)
hre : IsBoundedUnder (fun x1 x2 => x1 ≤ x2) atTop fun x => ‖f ↑x‖
him : ∀ (x : ℝ), ‖f (↑x * I)‖ ≤ C
hz : 0 ≤ z✝.re
ε : ℝ
ε₀ : ε < 0
g : ℂ → E := fun z => cexp (↑ε * z) • f z
hd : DiffContOnCl ℂ g {z | 0 < z.re}
z : ℂ
⊢ ‖g z‖ = expR (ε * z.re) * ‖f z‖

Tactic:
rw [norm_smul, norm_exp, re_ofReal_mul]

Result:
no goals

Proof state:
case h.refine_1
E : Type u_1
inst✝¹ : NormedAddCommGroup E
inst✝ : NormedSpace ℂ E
C : ℝ
f : ℂ → E
z : ℂ
hexp : ∃ c < 2, ∃ B, f =O[cobounded ℂ ⊓ 𝓟 {z | 0 < z.re}] fun z => expR (B * ‖z‖ ^ c)
hre : IsBoundedUnder (fun x1 x2 => x1 ≤ x2) atTop fun x => ‖f ↑x‖
him : ∀ (x : ℝ), ‖f (↑x * I)‖ ≤ C
hz : 0 ≤ z.re
ε : ℝ
ε₀ : ε < 0
g : ℂ → E := fun z => cexp (↑ε * z) • f z
hd : DiffContOnCl ℂ g {z | 0 < z.re}
hgn : ∀ (z : ℂ), ‖g z‖ = expR (ε * z.re) * ‖f z‖
⊢ ∃ c < 2, ∃ B, g =O[cobounded ℂ ⊓ 𝓟 {z | 0 < z.re}] fun z => expR (B * ‖z‖ ^ c)

Tactic:
rcases hexp with ⟨c, hc, B, hO⟩

Result:
case h.refine_1.intro.intro.intro
E : Type u_1
inst✝¹ : NormedAddCommGroup E
inst✝ : NormedSpace ℂ E
C : ℝ
f : ℂ → E
z : ℂ
hre : IsBoundedUnder (fun x1 x2 => x1 ≤ x2) atTop fun x => ‖f ↑x‖
him : ∀ (x : ℝ), ‖f (↑x * I)‖ ≤ C
hz : 0 ≤ z.re
ε : ℝ
ε₀ : ε < 0
g : ℂ → E := fun z => cexp (↑ε * z) • f z
hd : DiffContOnCl ℂ g {z | 0 < z.re}
hgn : ∀ (z : ℂ), ‖g z‖ = expR (ε * z.re) * ‖f z‖
c : ℝ
hc : c < 2
B : ℝ
hO : f =O[cobounded ℂ ⊓ 𝓟 {z | 0 < z.re}] fun z => expR (B * ‖z‖ ^ c)
⊢ ∃ c < 2, ∃ B, g =O[cobounded ℂ ⊓ 𝓟 {z | 0 < z.re}] fun z => expR (B * ‖z‖ ^ c)

Proof state:
case h
E : Type u_1
inst✝¹ : NormedAddCommGroup E
inst✝ : NormedSpace ℂ E
C : ℝ
f : ℂ → E
z : ℂ
hd : DiffContOnCl ℂ f {z | 0 < z.re}
hexp : ∃ c < 2, ∃ B, f =O[cobounded ℂ ⊓ 𝓟 {z | 0 < z.re}] fun z => expR (B * ‖z‖ ^ c)
hre : IsBoundedUnder (fun x1 x2 => x1 ≤ x2) atTop fun x => ‖f ↑x‖
him : ∀ (x : ℝ), ‖f (↑x * I)‖ ≤ C
hz : 0 ≤ z.re
this : ∀ᶠ (ε : ℝ) in 𝓝[<] 0, ‖cexp (↑ε * z) • f z‖ ≤ C
⊢ ‖cexp (↑0 * z) • f z‖ = ‖f z‖

Tactic:
simp

Result:
no goals

Proof state:
case h.refine_1.intro.intro.intro
E : Type u_1
inst✝¹ : NormedAddCommGroup E
inst✝ : NormedSpace ℂ E
C : ℝ
f : ℂ → E
z✝ : ℂ
hre : IsBoundedUnder (fun x1 x2 => x1 ≤ x2) atTop fun x => ‖f ↑x‖
him : ∀ (x : ℝ), ‖f (↑x * I)‖ ≤ C
hz✝ : 0 ≤ z✝.re
ε : ℝ
ε₀ : ε < 0
g : ℂ → E := fun z => cexp (↑ε * z) • f z
hd : DiffContOnCl ℂ g {z | 0 < z.re}
hgn : ∀ (z : ℂ), ‖g z‖ = expR (ε * z.re) * ‖f z‖
c : ℝ
hc : c < 2
B : ℝ
hO : f =O[cobounded ℂ ⊓ 𝓟 {z | 0 < z.re}] fun z => expR (B * ‖z‖ ^ c)
z : ℂ
hz : z ∈ {z | 0 < z.re}
⊢ expR (ε * z.re) * ‖f z‖ ≤ ‖f z‖

Tactic:
refine mul_le_of_le_one_left (norm_nonneg _) (Real.exp_le_one_iff.2 ?_)

Result:
case h.refine_1.intro.intro.intro
E : Type u_1
inst✝¹ : NormedAddCommGroup E
inst✝ : NormedSpace ℂ E
C : ℝ
f : ℂ → E
z✝ : ℂ
hre : IsBoundedUnder (fun x1 x2 => x1 ≤ x2) atTop fun x => ‖f ↑x‖
him : ∀ (x : ℝ), ‖f (↑x * I)‖ ≤ C
hz✝ : 0 ≤ z✝.re
ε : ℝ
ε₀ : ε < 0
g : ℂ → E := fun z => cexp (↑ε * z) • f z
hd : DiffContOnCl ℂ g {z | 0 < z.re}
hgn : ∀ (z : ℂ), ‖g z‖ = expR (ε * z.re) * ‖f z‖
c : ℝ
hc : c < 2
B : ℝ
hO : f =O[cobounded ℂ ⊓ 𝓟 {z | 0 < z.re}] fun z => expR (B * ‖z‖ ^ c)
z : ℂ
hz : z ∈ {z | 0 < z.re}
⊢ ε * z.re ≤ 0

Proof state:
E : Type u_1
inst✝¹ : NormedAddCommGroup E
inst✝ : NormedSpace ℂ E
C : ℝ
f : ℂ → E
z : ℂ
hd : DiffContOnCl ℂ f {z | 0 < z.re}
hexp : ∃ c < 2, ∃ B, f =O[cobounded ℂ ⊓ 𝓟 {z | 0 < z.re}] fun z => expR (B * ‖z‖ ^ c)
hre : IsBoundedUnder (fun x1 x2 => x1 ≤ x2) atTop fun x => ‖f ↑x‖
him : ∀ (x : ℝ), ‖f (↑x * I)‖ ≤ C
hz : 0 ≤ z.re
this : ∀ᶠ (ε : ℝ) in 𝓝[<] 0, ‖cexp (↑ε * z) • f z‖ ≤ C
⊢ ‖f z‖ ≤ C

Tactic:
refine le_of_tendsto (Tendsto.mono_left ?_ nhdsWithin_le_nhds) this

Result:
E : Type u_1
inst✝¹ : NormedAddCommGroup E
inst✝ : NormedSpace ℂ E
C : ℝ
f : ℂ → E
z : ℂ
hd : DiffContOnCl ℂ f {z | 0 < z.re}
hexp : ∃ c < 2, ∃ B, f =O[cobounded ℂ ⊓ 𝓟 {z | 0 < z.re}] fun z => expR (B * ‖z‖ ^ c)
hre : IsBoundedUnder (fun x1 x2 => x1 ≤ x2) atTop fun x => ‖f ↑x‖
him : ∀ (x : ℝ), ‖f (↑x * I)‖ ≤ C
hz : 0 ≤ z.re
this : ∀ᶠ (ε : ℝ) in 𝓝[<] 0, ‖cexp (↑ε * z) • f z‖ ≤ C
⊢ Tendsto (fun c => ‖cexp (↑c * z) • f z‖) (𝓝 0) (𝓝 ‖f z‖)

Proof state:
case h.refine_1.intro.intro.intro
E : Type u_1
inst✝¹ : NormedAddCommGroup E
inst✝ : NormedSpace ℂ E
C : ℝ
f : ℂ → E
z✝ : ℂ
hre : IsBoundedUnder (fun x1 x2 => x1 ≤ x2) atTop fun x => ‖f ↑x‖
him : ∀ (x : ℝ), ‖f (↑x * I)‖ ≤ C
hz✝ : 0 ≤ z✝.re
ε : ℝ
ε₀ : ε < 0
g : ℂ → E := fun z => cexp (↑ε * z) • f z
hd : DiffContOnCl ℂ g {z | 0 < z.re}
hgn : ∀ (z : ℂ), ‖g z‖ = expR (ε * z.re) * ‖f z‖
c : ℝ
hc : c < 2
B : ℝ
hO : f =O[cobounded ℂ ⊓ 𝓟 {z | 0 < z.re}] fun z => expR (B * ‖z‖ ^ c)
z : ℂ
hz : z ∈ {z | 0 < z.re}
⊢ ‖g z‖ ≤ ‖f z‖

Tactic:
rw [hgn]

Result:
case h.refine_1.intro.intro.intro
E : Type u_1
inst✝¹ : NormedAddCommGroup E
inst✝ : NormedSpace ℂ E
C : ℝ
f : ℂ → E
z✝ : ℂ
hre : IsBoundedUnder (fun x1 x2 => x1 ≤ x2) atTop fun x => ‖f ↑x‖
him : ∀ (x : ℝ), ‖f (↑x * I)‖ ≤ C
hz✝ : 0 ≤ z✝.re
ε : ℝ
ε₀ : ε < 0
g : ℂ → E := fun z => cexp (↑ε * z) • f z
hd : DiffContOnCl ℂ g {z | 0 < z.re}
hgn : ∀ (z : ℂ), ‖g z‖ = expR (ε * z.re) * ‖f z‖
c : ℝ
hc : c < 2
B : ℝ
hO : f =O[cobounded ℂ ⊓ 𝓟 {z | 0 < z.re}] fun z => expR (B * ‖z‖ ^ c)
z : ℂ
hz : z ∈ {z | 0 < z.re}
⊢ expR (ε * z.re) * ‖f z‖ ≤ ‖f z‖

Proof state:
E : Type u_1
inst✝¹ : NormedAddCommGroup E
inst✝ : NormedSpace ℂ E
C : ℝ
f : ℂ → E
z : ℂ
hd : DiffContOnCl ℂ f {z | 0 < z.re}
hexp : ∃ c < 2, ∃ B, f =O[cobounded ℂ ⊓ 𝓟 {z | 0 < z.re}] fun z => expR (B * ‖z‖ ^ c)
hre : IsBoundedUnder (fun x1 x2 => x1 ≤ x2) atTop fun x => ‖f ↑x‖
him : ∀ (x : ℝ), ‖f (↑x * I)‖ ≤ C
hz : 0 ≤ z.re
this : ∀ᶠ (ε : ℝ) in 𝓝[<] 0, ‖cexp (↑ε * z) • f z‖ ≤ C
⊢ Tendsto (fun c => ‖cexp (↑c * z) • f z‖) (𝓝 0) (𝓝 ‖f z‖)

Tactic:
apply ((continuous_ofReal.mul continuous_const).cexp.smul continuous_const).norm.tendsto'

Result:
case h
E : Type u_1
inst✝¹ : NormedAddCommGroup E
inst✝ : NormedSpace ℂ E
C : ℝ
f : ℂ → E
z : ℂ
hd : DiffContOnCl ℂ f {z | 0 < z.re}
hexp : ∃ c < 2, ∃ B, f =O[cobounded ℂ ⊓ 𝓟 {z | 0 < z.re}] fun z => expR (B * ‖z‖ ^ c)
hre : IsBoundedUnder (fun x1 x2 => x1 ≤ x2) atTop fun x => ‖f ↑x‖
him : ∀ (x : ℝ), ‖f (↑x * I)‖ ≤ C
hz : 0 ≤ z.re
this : ∀ᶠ (ε : ℝ) in 𝓝[<] 0, ‖cexp (↑ε * z) • f z‖ ≤ C
⊢ ‖cexp (↑0 * z) • f z‖ = ‖f z‖

Proof state:
case h.refine_2
E : Type u_1
inst✝¹ : NormedAddCommGroup E
inst✝ : NormedSpace ℂ E
C : ℝ
f : ℂ → E
z : ℂ
hexp : ∃ c < 2, ∃ B, f =O[cobounded ℂ ⊓ 𝓟 {z | 0 < z.re}] fun z => expR (B * ‖z‖ ^ c)
hre : IsBoundedUnder (fun x1 x2 => x1 ≤ x2) atTop fun x => ‖f ↑x‖
him : ∀ (x : ℝ), ‖f (↑x * I)‖ ≤ C
hz : 0 ≤ z.re
ε : ℝ
ε₀ : ε < 0
g : ℂ → E := fun z => cexp (↑ε * z) • f z
hd : DiffContOnCl ℂ g {z | 0 < z.re}
hgn : ∀ (z : ℂ), ‖g z‖ = expR (ε * z.re) * ‖f z‖
⊢ Tendsto (fun x => expR (ε * x) • f ↑x) atTop (𝓝 0)

Tactic:
have h₀ : Tendsto (fun x : ℝ => expR (ε * x)) atTop (𝓝 0) :=
  Real.tendsto_exp_atBot.comp (tendsto_const_nhds.neg_mul_atTop ε₀ tendsto_id)

Result:
case h.refine_2
E : Type u_1
inst✝¹ : NormedAddCommGroup E
inst✝ : NormedSpace ℂ E
C : ℝ
f : ℂ → E
z : ℂ
hexp : ∃ c < 2, ∃ B, f =O[cobounded ℂ ⊓ 𝓟 {z | 0 < z.re}] fun z => expR (B * ‖z‖ ^ c)
hre : IsBoundedUnder (fun x1 x2 => x1 ≤ x2) atTop fun x => ‖f ↑x‖
him : ∀ (x : ℝ), ‖f (↑x * I)‖ ≤ C
hz : 0 ≤ z.re
ε : ℝ
ε₀ : ε < 0
g : ℂ → E := fun z => cexp (↑ε * z) • f z
hd : DiffContOnCl ℂ g {z | 0 < z.re}
hgn : ∀ (z : ℂ), ‖g z‖ = expR (ε * z.re) * ‖f z‖
h₀ : Tendsto (fun x => expR (ε * x)) atTop (𝓝 0)
⊢ Tendsto (fun x => expR (ε * x) • f ↑x) atTop (𝓝 0)