-- Mathlib/Analysis/Calculus/FDeriv/RestrictScalars.lean
theorem differentiableWithinAt_iff_restrictScalars (hf : DifferentiableWithinAt 𝕜 f s x)
    (hs : UniqueDiffWithinAt 𝕜 s x) : DifferentiableWithinAt 𝕜' f s x ↔
      ∃ g' : E →L[𝕜'] F, g'.restrictScalars 𝕜 = fderivWithin 𝕜 f s x

Proof state:
case mp
𝕜 : Type u_1
inst✝¹⁰ : NontriviallyNormedField 𝕜
𝕜' : Type u_2
inst✝⁹ : NontriviallyNormedField 𝕜'
inst✝⁸ : NormedAlgebra 𝕜 𝕜'
E : Type u_3
inst✝⁷ : NormedAddCommGroup E
inst✝⁶ : NormedSpace 𝕜 E
inst✝⁵ : NormedSpace 𝕜' E
inst✝⁴ : IsScalarTower 𝕜 𝕜' E
F : Type u_4
inst✝³ : NormedAddCommGroup F
inst✝² : NormedSpace 𝕜 F
inst✝¹ : NormedSpace 𝕜' F
inst✝ : IsScalarTower 𝕜 𝕜' F
f : E → F
s : Set E
x : E
hf : DifferentiableWithinAt 𝕜 f s x
hs : UniqueDiffWithinAt 𝕜 s x
⊢ DifferentiableWithinAt 𝕜' f s x → ∃ g', restrictScalars 𝕜 g' = fderivWithin 𝕜 f s x

Tactic:
rintro ⟨g', hg'⟩

Result:
case mp.intro
𝕜 : Type u_1
inst✝¹⁰ : NontriviallyNormedField 𝕜
𝕜' : Type u_2
inst✝⁹ : NontriviallyNormedField 𝕜'
inst✝⁸ : NormedAlgebra 𝕜 𝕜'
E : Type u_3
inst✝⁷ : NormedAddCommGroup E
inst✝⁶ : NormedSpace 𝕜 E
inst✝⁵ : NormedSpace 𝕜' E
inst✝⁴ : IsScalarTower 𝕜 𝕜' E
F : Type u_4
inst✝³ : NormedAddCommGroup F
inst✝² : NormedSpace 𝕜 F
inst✝¹ : NormedSpace 𝕜' F
inst✝ : IsScalarTower 𝕜 𝕜' F
f : E → F
s : Set E
x : E
hf : DifferentiableWithinAt 𝕜 f s x
hs : UniqueDiffWithinAt 𝕜 s x
g' : E →L[𝕜'] F
hg' : HasFDerivWithinAt f g' s x
⊢ ∃ g', restrictScalars 𝕜 g' = fderivWithin 𝕜 f s x

Proof state:
case mp.intro
𝕜 : Type u_1
inst✝¹⁰ : NontriviallyNormedField 𝕜
𝕜' : Type u_2
inst✝⁹ : NontriviallyNormedField 𝕜'
inst✝⁸ : NormedAlgebra 𝕜 𝕜'
E : Type u_3
inst✝⁷ : NormedAddCommGroup E
inst✝⁶ : NormedSpace 𝕜 E
inst✝⁵ : NormedSpace 𝕜' E
inst✝⁴ : IsScalarTower 𝕜 𝕜' E
F : Type u_4
inst✝³ : NormedAddCommGroup F
inst✝² : NormedSpace 𝕜 F
inst✝¹ : NormedSpace 𝕜' F
inst✝ : IsScalarTower 𝕜 𝕜' F
f : E → F
s : Set E
x : E
hf : DifferentiableWithinAt 𝕜 f s x
hs : UniqueDiffWithinAt 𝕜 s x
g' : E →L[𝕜'] F
hg' : HasFDerivWithinAt f g' s x
⊢ ∃ g', restrictScalars 𝕜 g' = fderivWithin 𝕜 f s x

Tactic:
exact ⟨g', hs.eq (hg'.restrictScalars 𝕜) hf.hasFDerivWithinAt⟩

Result:
no goals

Proof state:
case mpr.intro
𝕜 : Type u_1
inst✝¹⁰ : NontriviallyNormedField 𝕜
𝕜' : Type u_2
inst✝⁹ : NontriviallyNormedField 𝕜'
inst✝⁸ : NormedAlgebra 𝕜 𝕜'
E : Type u_3
inst✝⁷ : NormedAddCommGroup E
inst✝⁶ : NormedSpace 𝕜 E
inst✝⁵ : NormedSpace 𝕜' E
inst✝⁴ : IsScalarTower 𝕜 𝕜' E
F : Type u_4
inst✝³ : NormedAddCommGroup F
inst✝² : NormedSpace 𝕜 F
inst✝¹ : NormedSpace 𝕜' F
inst✝ : IsScalarTower 𝕜 𝕜' F
f : E → F
s : Set E
x : E
hf : DifferentiableWithinAt 𝕜 f s x
hs : UniqueDiffWithinAt 𝕜 s x
f' : E →L[𝕜'] F
hf' : restrictScalars 𝕜 f' = fderivWithin 𝕜 f s x
⊢ DifferentiableWithinAt 𝕜' f s x

Tactic:
exact ⟨f', hf.hasFDerivWithinAt.of_restrictScalars 𝕜 hf'⟩

Result:
no goals

Proof state:
case mpr
𝕜 : Type u_1
inst✝¹⁰ : NontriviallyNormedField 𝕜
𝕜' : Type u_2
inst✝⁹ : NontriviallyNormedField 𝕜'
inst✝⁸ : NormedAlgebra 𝕜 𝕜'
E : Type u_3
inst✝⁷ : NormedAddCommGroup E
inst✝⁶ : NormedSpace 𝕜 E
inst✝⁵ : NormedSpace 𝕜' E
inst✝⁴ : IsScalarTower 𝕜 𝕜' E
F : Type u_4
inst✝³ : NormedAddCommGroup F
inst✝² : NormedSpace 𝕜 F
inst✝¹ : NormedSpace 𝕜' F
inst✝ : IsScalarTower 𝕜 𝕜' F
f : E → F
s : Set E
x : E
hf : DifferentiableWithinAt 𝕜 f s x
hs : UniqueDiffWithinAt 𝕜 s x
⊢ (∃ g', restrictScalars 𝕜 g' = fderivWithin 𝕜 f s x) → DifferentiableWithinAt 𝕜' f s x

Tactic:
rintro ⟨f', hf'⟩

Result:
case mpr.intro
𝕜 : Type u_1
inst✝¹⁰ : NontriviallyNormedField 𝕜
𝕜' : Type u_2
inst✝⁹ : NontriviallyNormedField 𝕜'
inst✝⁸ : NormedAlgebra 𝕜 𝕜'
E : Type u_3
inst✝⁷ : NormedAddCommGroup E
inst✝⁶ : NormedSpace 𝕜 E
inst✝⁵ : NormedSpace 𝕜' E
inst✝⁴ : IsScalarTower 𝕜 𝕜' E
F : Type u_4
inst✝³ : NormedAddCommGroup F
inst✝² : NormedSpace 𝕜 F
inst✝¹ : NormedSpace 𝕜' F
inst✝ : IsScalarTower 𝕜 𝕜' F
f : E → F
s : Set E
x : E
hf : DifferentiableWithinAt 𝕜 f s x
hs : UniqueDiffWithinAt 𝕜 s x
f' : E →L[𝕜'] F
hf' : restrictScalars 𝕜 f' = fderivWithin 𝕜 f s x
⊢ DifferentiableWithinAt 𝕜' f s x

Proof state:
𝕜 : Type u_1
inst✝¹⁰ : NontriviallyNormedField 𝕜
𝕜' : Type u_2
inst✝⁹ : NontriviallyNormedField 𝕜'
inst✝⁸ : NormedAlgebra 𝕜 𝕜'
E : Type u_3
inst✝⁷ : NormedAddCommGroup E
inst✝⁶ : NormedSpace 𝕜 E
inst✝⁵ : NormedSpace 𝕜' E
inst✝⁴ : IsScalarTower 𝕜 𝕜' E
F : Type u_4
inst✝³ : NormedAddCommGroup F
inst✝² : NormedSpace 𝕜 F
inst✝¹ : NormedSpace 𝕜' F
inst✝ : IsScalarTower 𝕜 𝕜' F
f : E → F
s : Set E
x : E
hf : DifferentiableWithinAt 𝕜 f s x
hs : UniqueDiffWithinAt 𝕜 s x
⊢ DifferentiableWithinAt 𝕜' f s x ↔ ∃ g', restrictScalars 𝕜 g' = fderivWithin 𝕜 f s x

Tactic:
constructor

Result:
case mp
𝕜 : Type u_1
inst✝¹⁰ : NontriviallyNormedField 𝕜
𝕜' : Type u_2
inst✝⁹ : NontriviallyNormedField 𝕜'
inst✝⁸ : NormedAlgebra 𝕜 𝕜'
E : Type u_3
inst✝⁷ : NormedAddCommGroup E
inst✝⁶ : NormedSpace 𝕜 E
inst✝⁵ : NormedSpace 𝕜' E
inst✝⁴ : IsScalarTower 𝕜 𝕜' E
F : Type u_4
inst✝³ : NormedAddCommGroup F
inst✝² : NormedSpace 𝕜 F
inst✝¹ : NormedSpace 𝕜' F
inst✝ : IsScalarTower 𝕜 𝕜' F
f : E → F
s : Set E
x : E
hf : DifferentiableWithinAt 𝕜 f s x
hs : UniqueDiffWithinAt 𝕜 s x
⊢ DifferentiableWithinAt 𝕜' f s x → ∃ g', restrictScalars 𝕜 g' = fderivWithin 𝕜 f s x

case mpr
𝕜 : Type u_1
inst✝¹⁰ : NontriviallyNormedField 𝕜
𝕜' : Type u_2
inst✝⁹ : NontriviallyNormedField 𝕜'
inst✝⁸ : NormedAlgebra 𝕜 𝕜'
E : Type u_3
inst✝⁷ : NormedAddCommGroup E
inst✝⁶ : NormedSpace 𝕜 E
inst✝⁵ : NormedSpace 𝕜' E
inst✝⁴ : IsScalarTower 𝕜 𝕜' E
F : Type u_4
inst✝³ : NormedAddCommGroup F
inst✝² : NormedSpace 𝕜 F
inst✝¹ : NormedSpace 𝕜' F
inst✝ : IsScalarTower 𝕜 𝕜' F
f : E → F
s : Set E
x : E
hf : DifferentiableWithinAt 𝕜 f s x
hs : UniqueDiffWithinAt 𝕜 s x
⊢ (∃ g', restrictScalars 𝕜 g' = fderivWithin 𝕜 f s x) → DifferentiableWithinAt 𝕜' f s x