-- Mathlib/Computability/AkraBazzi/AkraBazzi.lean
lemma rpow_p_mul_one_sub_smoothingFn_le :
    ∀ᶠ (n : ℕ) in atTop, ∀ i, (r i n) ^ (p a b) * (1 - ε (r i n))
      ≤ (b i) ^ (p a b) * n ^ (p a b) * (1 - ε n)

Proof state:
α : Type u_1
inst✝¹ : Fintype α
T : ℕ → ℝ
g : ℝ → ℝ
a b : α → ℝ
r : α → ℕ → ℕ
inst✝ : Nonempty α
R : AkraBazziRecurrence T g a b r
i : α
q : ℝ → ℝ := fun x => x ^ p a b * (1 - ε x)
h_diff_q : DifferentiableOn ℝ q (Set.Ioi 1)
h_deriv_q : deriv q =O[atTop] fun x => x ^ (p a b - 1)
h_main_norm :
  (fun n => ‖q ↑(r i n) - q (b i * ↑n)‖) ≤ᶠ[atTop] fun n => ‖b i ^ p a b * ↑n ^ p a b * (ε (b i * ↑n) - ε ↑n)‖
⊢ ∀ᶠ (x : ℕ) in atTop, ↑(r i x) ^ p a b * (1 - ε ↑(r i x)) ≤ b i ^ p a b * ↑x ^ p a b * (1 - ε ↑x)

Tactic:
have h_main : (fun (n : ℕ) => q (r i n) - q (b i * n))
    ≤ᶠ[atTop] fun (n : ℕ) => (b i) ^ (p a b) * n ^ (p a b) * (ε (b i * n) - ε n) := by
  calc (fun (n : ℕ) => q (r i n) - q (b i * n))
         ≤ᶠ[atTop] fun (n : ℕ) => ‖q (r i n) - q (b i * n)‖ := by
              filter_upwards with _; exact le_norm_self _
       _ ≤ᶠ[atTop] fun (n : ℕ) => ‖(b i) ^ (p a b) * n ^ (p a b) * (ε (b i * n) - ε n)‖ :=
              h_main_norm
       _ =ᶠ[atTop] fun (n : ℕ) => (b i) ^ (p a b) * n ^ (p a b) * (ε (b i * n) - ε n) := by
              filter_upwards [eventually_gt_atTop ⌈(b i)⁻¹⌉₊, eventually_gt_atTop 1] with n hn hn'
              refine norm_of_nonneg ?_
              have h₁ := R.b_pos i
              have h₂ : 0 ≤ ε (b i * n) - ε n := by
                refine sub_nonneg_of_le <|
                  (strictAntiOn_smoothingFn.le_iff_le ?n_gt_one ?bn_gt_one).mpr ?le
                case n_gt_one =>
                  rwa [Set.mem_Ioi, Nat.one_lt_cast]
                case bn_gt_one =>
                  calc 1 = b i * (b i)⁻¹ := by rw [mul_inv_cancel₀ (by positivity)]
                      _ ≤ b i * ⌈(b i)⁻¹⌉₊ := by gcongr; exact Nat.le_ceil _
                      _ < b i * n := by gcongr
                case le => calc b i * n ≤ 1 * n := by have := R.b_lt_one i; gcongr
                                        _ = n := by rw [one_mul]
              positivity

Result:
α : Type u_1
inst✝¹ : Fintype α
T : ℕ → ℝ
g : ℝ → ℝ
a b : α → ℝ
r : α → ℕ → ℕ
inst✝ : Nonempty α
R : AkraBazziRecurrence T g a b r
i : α
q : ℝ → ℝ := fun x => x ^ p a b * (1 - ε x)
h_diff_q : DifferentiableOn ℝ q (Set.Ioi 1)
h_deriv_q : deriv q =O[atTop] fun x => x ^ (p a b - 1)
h_main_norm :
  (fun n => ‖q ↑(r i n) - q (b i * ↑n)‖) ≤ᶠ[atTop] fun n => ‖b i ^ p a b * ↑n ^ p a b * (ε (b i * ↑n) - ε ↑n)‖
h_main : (fun n => q ↑(r i n) - q (b i * ↑n)) ≤ᶠ[atTop] fun n => b i ^ p a b * ↑n ^ p a b * (ε (b i * ↑n) - ε ↑n)
⊢ ∀ᶠ (x : ℕ) in atTop, ↑(r i x) ^ p a b * (1 - ε ↑(r i x)) ≤ b i ^ p a b * ↑x ^ p a b * (1 - ε ↑x)

Proof state:
α : Type u_1
inst✝¹ : Fintype α
T : ℕ → ℝ
g : ℝ → ℝ
a b : α → ℝ
r : α → ℕ → ℕ
inst✝ : Nonempty α
R : AkraBazziRecurrence T g a b r
i : α
q : ℝ → ℝ := fun x => x ^ p a b * (1 - ε x)
h_diff_q : DifferentiableOn ℝ q (Set.Ioi 1)
⊢ (fun x => deriv (fun z => z ^ p a b) x * (1 - ε x)) =O[atTop] fun x => x ^ (p a b - 1) * (1 - ε x)

Tactic:
exact IsBigO.mul (isBigO_deriv_rpow_const_atTop (p a b)) (isBigO_refl _ _)

Result:
no goals

Proof state:
α : Type u_1
inst✝¹ : Fintype α
T : ℕ → ℝ
g : ℝ → ℝ
a b : α → ℝ
r : α → ℕ → ℕ
inst✝ : Nonempty α
R : AkraBazziRecurrence T g a b r
i : α
q : ℝ → ℝ := fun x => x ^ p a b * (1 - ε x)
⊢ ∀ᶠ (x : ℕ) in atTop, ↑(r i x) ^ p a b * (1 - ε ↑(r i x)) ≤ b i ^ p a b * ↑x ^ p a b * (1 - ε ↑x)

Tactic:
have h_diff_q : DifferentiableOn ℝ q (Set.Ioi 1) := by
  refine DifferentiableOn.mul
    (DifferentiableOn.mono (differentiableOn_rpow_const _) fun z hz => ?_)
      differentiableOn_one_sub_smoothingFn
  rw [Set.mem_compl_singleton_iff]
  rw [Set.mem_Ioi] at hz
  exact ne_of_gt <| zero_lt_one.trans hz

Result:
α : Type u_1
inst✝¹ : Fintype α
T : ℕ → ℝ
g : ℝ → ℝ
a b : α → ℝ
r : α → ℕ → ℕ
inst✝ : Nonempty α
R : AkraBazziRecurrence T g a b r
i : α
q : ℝ → ℝ := fun x => x ^ p a b * (1 - ε x)
h_diff_q : DifferentiableOn ℝ q (Set.Ioi 1)
⊢ ∀ᶠ (x : ℕ) in atTop, ↑(r i x) ^ p a b * (1 - ε ↑(r i x)) ≤ b i ^ p a b * ↑x ^ p a b * (1 - ε ↑x)

Proof state:
α : Type u_1
inst✝¹ : Fintype α
T : ℕ → ℝ
g : ℝ → ℝ
a b : α → ℝ
r : α → ℕ → ℕ
inst✝ : Nonempty α
R : AkraBazziRecurrence T g a b r
i : α
q : ℝ → ℝ := fun x => x ^ p a b * (1 - ε x)
h_diff_q : DifferentiableOn ℝ q (Set.Ioi 1)
h_deriv_q : deriv q =O[atTop] fun x => x ^ (p a b - 1)
⊢ (fun n => deriv q ↑n * (↑n / log ↑n ^ 2)) =O[atTop] fun n => ↑n ^ (p a b - 1) * (↑n / log ↑n ^ 2)

Tactic:
exact IsBigO.mul (IsBigO.natCast_atTop h_deriv_q) (isBigO_refl _ _)

Result:
no goals

Proof state:
case h
α : Type u_1
inst✝¹ : Fintype α
T : ℕ → ℝ
g : ℝ → ℝ
a b : α → ℝ
r : α → ℕ → ℕ
inst✝ : Nonempty α
R : AkraBazziRecurrence T g a b r
i : α
q : ℝ → ℝ := fun x => x ^ p a b * (1 - ε x)
h_diff_q : DifferentiableOn ℝ q (Set.Ioi 1)
x✝ : ℝ
⊢ x✝ ^ (p a b - 1) * 1 = x✝ ^ (p a b - 1)

Tactic:
rw [mul_one]

Result:
no goals

Proof state:
α : Type u_1
inst✝¹ : Fintype α
T : ℕ → ℝ
g : ℝ → ℝ
a b : α → ℝ
r : α → ℕ → ℕ
inst✝ : Nonempty α
R : AkraBazziRecurrence T g a b r
i : α
q : ℝ → ℝ := fun x => x ^ p a b * (1 - ε x)
h_diff_q : DifferentiableOn ℝ q (Set.Ioi 1)
h_deriv_q : deriv q =O[atTop] fun x => x ^ (p a b - 1)
h_main_norm :
  (fun n => ‖q ↑(r i n) - q (b i * ↑n)‖) ≤ᶠ[atTop] fun n => ‖b i ^ p a b * ↑n ^ p a b * (ε (b i * ↑n) - ε ↑n)‖
h_main : (fun n => q ↑(r i n) - q (b i * ↑n)) ≤ᶠ[atTop] fun n => b i ^ p a b * ↑n ^ p a b * (ε (b i * ↑n) - ε ↑n)
⊢ ∀ᶠ (x : ℕ) in atTop, ↑(r i x) ^ p a b * (1 - ε ↑(r i x)) ≤ b i ^ p a b * ↑x ^ p a b * (1 - ε ↑x)

Tactic:
filter_upwards [h_main] with n hn

Result:
case h
α : Type u_1
inst✝¹ : Fintype α
T : ℕ → ℝ
g : ℝ → ℝ
a b : α → ℝ
r : α → ℕ → ℕ
inst✝ : Nonempty α
R : AkraBazziRecurrence T g a b r
i : α
q : ℝ → ℝ := fun x => x ^ p a b * (1 - ε x)
h_diff_q : DifferentiableOn ℝ q (Set.Ioi 1)
h_deriv_q : deriv q =O[atTop] fun x => x ^ (p a b - 1)
h_main_norm :
  (fun n => ‖q ↑(r i n) - q (b i * ↑n)‖) ≤ᶠ[atTop] fun n => ‖b i ^ p a b * ↑n ^ p a b * (ε (b i * ↑n) - ε ↑n)‖
h_main : (fun n => q ↑(r i n) - q (b i * ↑n)) ≤ᶠ[atTop] fun n => b i ^ p a b * ↑n ^ p a b * (ε (b i * ↑n) - ε ↑n)
n : ℕ
hn : q ↑(r i n) - q (b i * ↑n) ≤ b i ^ p a b * ↑n ^ p a b * (ε (b i * ↑n) - ε ↑n)
⊢ ↑(r i n) ^ p a b * (1 - ε ↑(r i n)) ≤ b i ^ p a b * ↑n ^ p a b * (1 - ε ↑n)