-- Mathlib/MeasureTheory/Integral/FundThmCalculus.lean
theorem integrableOn_deriv_right_of_nonneg (hcont : ContinuousOn g (Icc a b))
    (hderiv : ∀ x ∈ Ioo a b, HasDerivWithinAt g (g' x) (Ioi x) x)
    (g'pos : ∀ x ∈ Ioo a b, 0 ≤ g' x) : IntegrableOn g' (Ioc a b)

Proof state:
case pos
g' g : ℝ → ℝ
a b : ℝ
hcont : ContinuousOn g (Icc a b)
hderiv : ∀ x ∈ Ioo a b, HasDerivWithinAt g (g' x) (Ioi x) x
g'pos : ∀ x ∈ Ioo a b, 0 ≤ g' x
hab : a < b
⊢ IntegrableOn g' (Ioc a b) volume

Tactic:
rw [integrableOn_Ioc_iff_integrableOn_Ioo]

Result:
case pos
g' g : ℝ → ℝ
a b : ℝ
hcont : ContinuousOn g (Icc a b)
hderiv : ∀ x ∈ Ioo a b, HasDerivWithinAt g (g' x) (Ioi x) x
g'pos : ∀ x ∈ Ioo a b, 0 ≤ g' x
hab : a < b
⊢ IntegrableOn g' (Ioo a b) volume

Proof state:
g' g : ℝ → ℝ
a b : ℝ
hcont : ContinuousOn g (Icc a b)
hderiv : ∀ x ∈ Ioo a b, HasDerivWithinAt g (g' x) (Ioi x) x
g'pos : ∀ x ∈ Ioo a b, 0 ≤ g' x
⊢ IntegrableOn g' (Ioc a b) volume

Tactic:
by_cases hab : a < b

Result:
case pos
g' g : ℝ → ℝ
a b : ℝ
hcont : ContinuousOn g (Icc a b)
hderiv : ∀ x ∈ Ioo a b, HasDerivWithinAt g (g' x) (Ioi x) x
g'pos : ∀ x ∈ Ioo a b, 0 ≤ g' x
hab : a < b
⊢ IntegrableOn g' (Ioc a b) volume

case neg
g' g : ℝ → ℝ
a b : ℝ
hcont : ContinuousOn g (Icc a b)
hderiv : ∀ x ∈ Ioo a b, HasDerivWithinAt g (g' x) (Ioi x) x
g'pos : ∀ x ∈ Ioo a b, 0 ≤ g' x
hab : ¬a < b
⊢ IntegrableOn g' (Ioc a b) volume

Proof state:
g' g : ℝ → ℝ
a b : ℝ
hcont : ContinuousOn g (Icc a b)
hderiv : ∀ x ∈ Ioo a b, HasDerivWithinAt g (g' x) (Ioi x) x
g'pos : ∀ x ∈ Ioo a b, 0 ≤ g' x
hab : a < b
x : ℝ
hx : x ∈ Ioo a b
⊢ (fun x => derivWithin g (Ioi x) x) x = g' x

Tactic:
exact (hderiv x hx).derivWithin (uniqueDiffWithinAt_Ioi _)

Result:
no goals

Proof state:
g' g : ℝ → ℝ
a b : ℝ
hcont : ContinuousOn g (Icc a b)
hderiv : ∀ x ∈ Ioo a b, HasDerivWithinAt g (g' x) (Ioi x) x
g'pos : ∀ x ∈ Ioo a b, 0 ≤ g' x
hab : a < b
⊢ AEMeasurable g' (volume.restrict (Ioo a b))

Tactic:
apply (aemeasurable_derivWithin_Ioi g _).congr

Result:
g' g : ℝ → ℝ
a b : ℝ
hcont : ContinuousOn g (Icc a b)
hderiv : ∀ x ∈ Ioo a b, HasDerivWithinAt g (g' x) (Ioi x) x
g'pos : ∀ x ∈ Ioo a b, 0 ≤ g' x
hab : a < b
⊢ (fun x => derivWithin g (Ioi x) x) =ᶠ[ae (volume.restrict (Ioo a b))] g'

Proof state:
case pos.intro.intro.intro
g' g : ℝ → ℝ
a b : ℝ
hcont : ContinuousOn g (Icc a b)
hderiv : ∀ x ∈ Ioo a b, HasDerivWithinAt g (g' x) (Ioi x) x
g'pos : ∀ x ∈ Ioo a b, 0 ≤ g' x
hab : a < b
meas_g' : AEMeasurable g' (volume.restrict (Ioo a b))
H : ENNReal.ofReal (g b - g a) < ∫⁻ (x : ℝ) in Ioo a b, ↑‖g' x‖₊
f : SimpleFunc ℝ ℝ≥0
fle : ∀ (x : ℝ), f x ≤ ‖g' x‖₊
fint : ∫⁻ (x : ℝ) in Ioo a b, ↑(f x) < ⊤
hf : ENNReal.ofReal (g b - g a) < ∫⁻ (x : ℝ) in Ioo a b, ↑(f x)
F : ℝ → ℝ := NNReal.toReal ∘ ⇑f
⊢ False

Tactic:
have intF : IntegrableOn F (Ioo a b) := by
  refine ⟨f.measurable.coe_nnreal_real.aestronglyMeasurable, ?_⟩
  simpa only [F, hasFiniteIntegral_iff_enorm, comp_apply, NNReal.enorm_eq] using fint

Result:
case pos.intro.intro.intro
g' g : ℝ → ℝ
a b : ℝ
hcont : ContinuousOn g (Icc a b)
hderiv : ∀ x ∈ Ioo a b, HasDerivWithinAt g (g' x) (Ioi x) x
g'pos : ∀ x ∈ Ioo a b, 0 ≤ g' x
hab : a < b
meas_g' : AEMeasurable g' (volume.restrict (Ioo a b))
H : ENNReal.ofReal (g b - g a) < ∫⁻ (x : ℝ) in Ioo a b, ↑‖g' x‖₊
f : SimpleFunc ℝ ℝ≥0
fle : ∀ (x : ℝ), f x ≤ ‖g' x‖₊
fint : ∫⁻ (x : ℝ) in Ioo a b, ↑(f x) < ⊤
hf : ENNReal.ofReal (g b - g a) < ∫⁻ (x : ℝ) in Ioo a b, ↑(f x)
F : ℝ → ℝ := NNReal.toReal ∘ ⇑f
intF : IntegrableOn F (Ioo a b) volume
⊢ False

Proof state:
case pos.intro.intro.intro
g' g : ℝ → ℝ
a b : ℝ
hcont : ContinuousOn g (Icc a b)
hderiv : ∀ x ∈ Ioo a b, HasDerivWithinAt g (g' x) (Ioi x) x
g'pos : ∀ x ∈ Ioo a b, 0 ≤ g' x
hab : a < b
meas_g' : AEMeasurable g' (volume.restrict (Ioo a b))
H : ENNReal.ofReal (g b - g a) < ∫⁻ (x : ℝ) in Ioo a b, ↑‖g' x‖₊
f : SimpleFunc ℝ ℝ≥0
fle : ∀ (x : ℝ), f x ≤ ‖g' x‖₊
fint : ∫⁻ (x : ℝ) in Ioo a b, ↑(f x) < ⊤
hf : ENNReal.ofReal (g b - g a) < ∫⁻ (x : ℝ) in Ioo a b, ↑(f x)
F : ℝ → ℝ := NNReal.toReal ∘ ⇑f
intF : IntegrableOn F (Ioo a b) volume
A : ∫⁻ (x : ℝ) in Ioo a b, ↑(f x) = ENNReal.ofReal (∫ (x : ℝ) in Ioo a b, F x)
⊢ False

Tactic:
rw [A] at hf

Result:
case pos.intro.intro.intro
g' g : ℝ → ℝ
a b : ℝ
hcont : ContinuousOn g (Icc a b)
hderiv : ∀ x ∈ Ioo a b, HasDerivWithinAt g (g' x) (Ioi x) x
g'pos : ∀ x ∈ Ioo a b, 0 ≤ g' x
hab : a < b
meas_g' : AEMeasurable g' (volume.restrict (Ioo a b))
H : ENNReal.ofReal (g b - g a) < ∫⁻ (x : ℝ) in Ioo a b, ↑‖g' x‖₊
f : SimpleFunc ℝ ℝ≥0
fle : ∀ (x : ℝ), f x ≤ ‖g' x‖₊
fint : ∫⁻ (x : ℝ) in Ioo a b, ↑(f x) < ⊤
F : ℝ → ℝ := NNReal.toReal ∘ ⇑f
hf : ENNReal.ofReal (g b - g a) < ENNReal.ofReal (∫ (x : ℝ) in Ioo a b, F x)
intF : IntegrableOn F (Ioo a b) volume
A : ∫⁻ (x : ℝ) in Ioo a b, ↑(f x) = ENNReal.ofReal (∫ (x : ℝ) in Ioo a b, F x)
⊢ False

Proof state:
case pos.intro.intro.intro
g' g : ℝ → ℝ
a b : ℝ
hcont : ContinuousOn g (Icc a b)
hderiv : ∀ x ∈ Ioo a b, HasDerivWithinAt g (g' x) (Ioi x) x
g'pos : ∀ x ∈ Ioo a b, 0 ≤ g' x
hab : a < b
meas_g' : AEMeasurable g' (volume.restrict (Ioo a b))
H : ENNReal.ofReal (g b - g a) < ∫⁻ (x : ℝ) in Ioo a b, ↑‖g' x‖₊
f : SimpleFunc ℝ ℝ≥0
fle : ∀ (x : ℝ), f x ≤ ‖g' x‖₊
fint : ∫⁻ (x : ℝ) in Ioo a b, ↑(f x) < ⊤
F : ℝ → ℝ := NNReal.toReal ∘ ⇑f
hf : ENNReal.ofReal (g b - g a) < ENNReal.ofReal (∫ (x : ℝ) in Ioo a b, F x)
intF : IntegrableOn F (Ioo a b) volume
A : ∫⁻ (x : ℝ) in Ioo a b, ↑(f x) = ENNReal.ofReal (∫ (x : ℝ) in Ioo a b, F x)
B : ∫ (x : ℝ) in Ioo a b, F x ≤ g b - g a
⊢ False

Tactic:
exact lt_irrefl _ (hf.trans_le (ENNReal.ofReal_le_ofReal B))

Result:
no goals

Proof state:
g' g : ℝ → ℝ
a b : ℝ
hcont : ContinuousOn g (Icc a b)
hderiv : ∀ x ∈ Ioo a b, HasDerivWithinAt g (g' x) (Ioi x) x
g'pos : ∀ x ∈ Ioo a b, 0 ≤ g' x
hab : a < b
meas_g' : AEMeasurable g' (volume.restrict (Ioo a b))
H : ENNReal.ofReal (g b - g a) < ∫⁻ (x : ℝ) in Ioo a b, ↑‖g' x‖₊
f : SimpleFunc ℝ ℝ≥0
fle : ∀ (x : ℝ), f x ≤ ‖g' x‖₊
fint : ∫⁻ (x : ℝ) in Ioo a b, ↑(f x) < ⊤
F : ℝ → ℝ := NNReal.toReal ∘ ⇑f
hf : ENNReal.ofReal (g b - g a) < ENNReal.ofReal (∫ (x : ℝ) in Ioo a b, F x)
intF : IntegrableOn F (Ioo a b) volume
A : ∫⁻ (x : ℝ) in Ioo a b, ↑(f x) = ENNReal.ofReal (∫ (x : ℝ) in Ioo a b, F x)
⊢ ∫ (x : ℝ) in Ioo a b, F x ≤ g b - g a

Tactic:
rw [← integral_Ioc_eq_integral_Ioo, ← intervalIntegral.integral_of_le hab.le]

Result:
g' g : ℝ → ℝ
a b : ℝ
hcont : ContinuousOn g (Icc a b)
hderiv : ∀ x ∈ Ioo a b, HasDerivWithinAt g (g' x) (Ioi x) x
g'pos : ∀ x ∈ Ioo a b, 0 ≤ g' x
hab : a < b
meas_g' : AEMeasurable g' (volume.restrict (Ioo a b))
H : ENNReal.ofReal (g b - g a) < ∫⁻ (x : ℝ) in Ioo a b, ↑‖g' x‖₊
f : SimpleFunc ℝ ℝ≥0
fle : ∀ (x : ℝ), f x ≤ ‖g' x‖₊
fint : ∫⁻ (x : ℝ) in Ioo a b, ↑(f x) < ⊤
F : ℝ → ℝ := NNReal.toReal ∘ ⇑f
hf : ENNReal.ofReal (g b - g a) < ENNReal.ofReal (∫ (x : ℝ) in Ioo a b, F x)
intF : IntegrableOn F (Ioo a b) volume
A : ∫⁻ (x : ℝ) in Ioo a b, ↑(f x) = ENNReal.ofReal (∫ (x : ℝ) in Ioo a b, F x)
⊢ ∫ (x : ℝ) in a..b, F x ≤ g b - g a

Proof state:
case h.e'_4
g' g : ℝ → ℝ
a b : ℝ
hcont : ContinuousOn g (Icc a b)
hderiv : ∀ x ∈ Ioo a b, HasDerivWithinAt g (g' x) (Ioi x) x
g'pos : ∀ x ∈ Ioo a b, 0 ≤ g' x
hab : a < b
meas_g' : AEMeasurable g' (volume.restrict (Ioo a b))
H : ENNReal.ofReal (g b - g a) < ∫⁻ (x : ℝ) in Ioo a b, ↑‖g' x‖₊
f : SimpleFunc ℝ ℝ≥0
fle : ∀ (x : ℝ), f x ≤ ‖g' x‖₊
fint : ∫⁻ (x : ℝ) in Ioo a b, ↑(f x) < ⊤
F : ℝ → ℝ := NNReal.toReal ∘ ⇑f
hf : ENNReal.ofReal (g b - g a) < ENNReal.ofReal (∫ (x : ℝ) in Ioo a b, F x)
intF : IntegrableOn F (Ioo a b) volume
A : ∫⁻ (x : ℝ) in Ioo a b, ↑(f x) = ENNReal.ofReal (∫ (x : ℝ) in Ioo a b, F x)
x : ℝ
hx : x ∈ Ioo a b
⊢ g' x = ↑‖g' x‖₊

Tactic:
simp only [Real.norm_of_nonneg (g'pos x hx), coe_nnnorm]

Result:
no goals