-- Mathlib/Geometry/Manifold/Algebra/LeftInvariantDerivation.lean
theorem evalAt_mul : evalAt (g * h) X = 𝒅ₕ (L_apply I g h) (evalAt h X)

Proof state:
case H
𝕜 : Type u_1
inst✝⁷ : NontriviallyNormedField 𝕜
E : Type u_2
inst✝⁶ : NormedAddCommGroup E
inst✝⁵ : NormedSpace 𝕜 E
H : Type u_3
inst✝⁴ : TopologicalSpace H
I : ModelWithCorners 𝕜 E H
G : Type u_4
inst✝³ : TopologicalSpace G
inst✝² : ChartedSpace H G
inst✝¹ : Monoid G
inst✝ : ContMDiffMul I ∞ G
g h : G
X : LeftInvariantDerivation I G
f : C^∞⟮I, G; 𝕜⟯⟨g * h⟩
⊢ ((𝒅 (𝑳 I g) ((𝑳 I h) 1) ∘ₗ 𝒅 (𝑳 I h) 1) ((evalAt 1) X)) f = ((evalAt h) X) (ContMDiffMap.comp f (𝑳 I g))

Tactic:
erw [LinearMap.comp_apply]

Result:
case H
𝕜 : Type u_1
inst✝⁷ : NontriviallyNormedField 𝕜
E : Type u_2
inst✝⁶ : NormedAddCommGroup E
inst✝⁵ : NormedSpace 𝕜 E
H : Type u_3
inst✝⁴ : TopologicalSpace H
I : ModelWithCorners 𝕜 E H
G : Type u_4
inst✝³ : TopologicalSpace G
inst✝² : ChartedSpace H G
inst✝¹ : Monoid G
inst✝ : ContMDiffMul I ∞ G
g h : G
X : LeftInvariantDerivation I G
f : C^∞⟮I, G; 𝕜⟯⟨g * h⟩
⊢ ((𝒅 (𝑳 I g) ((𝑳 I h) 1)) ((𝒅 (𝑳 I h) 1) ((evalAt 1) X))) f = ((evalAt h) X) (ContMDiffMap.comp f (𝑳 I g))

Proof state:
𝕜 : Type u_1
inst✝⁷ : NontriviallyNormedField 𝕜
E : Type u_2
inst✝⁶ : NormedAddCommGroup E
inst✝⁵ : NormedSpace 𝕜 E
H : Type u_3
inst✝⁴ : TopologicalSpace H
I : ModelWithCorners 𝕜 E H
G : Type u_4
inst✝³ : TopologicalSpace G
inst✝² : ChartedSpace H G
inst✝¹ : Monoid G
inst✝ : ContMDiffMul I ∞ G
g h : G
X : LeftInvariantDerivation I G
⊢ (evalAt (g * h)) X = (𝒅ₕ ⋯) ((evalAt h) X)

Tactic:
ext f

Result:
case H
𝕜 : Type u_1
inst✝⁷ : NontriviallyNormedField 𝕜
E : Type u_2
inst✝⁶ : NormedAddCommGroup E
inst✝⁵ : NormedSpace 𝕜 E
H : Type u_3
inst✝⁴ : TopologicalSpace H
I : ModelWithCorners 𝕜 E H
G : Type u_4
inst✝³ : TopologicalSpace G
inst✝² : ChartedSpace H G
inst✝¹ : Monoid G
inst✝ : ContMDiffMul I ∞ G
g h : G
X : LeftInvariantDerivation I G
f : C^∞⟮I, G; 𝕜⟯⟨g * h⟩
⊢ ((evalAt (g * h)) X) f = ((𝒅ₕ ⋯) ((evalAt h) X)) f

Proof state:
case H
𝕜 : Type u_1
inst✝⁷ : NontriviallyNormedField 𝕜
E : Type u_2
inst✝⁶ : NormedAddCommGroup E
inst✝⁵ : NormedSpace 𝕜 E
H : Type u_3
inst✝⁴ : TopologicalSpace H
I : ModelWithCorners 𝕜 E H
G : Type u_4
inst✝³ : TopologicalSpace G
inst✝² : ChartedSpace H G
inst✝¹ : Monoid G
inst✝ : ContMDiffMul I ∞ G
g h : G
X : LeftInvariantDerivation I G
f : C^∞⟮I, G; 𝕜⟯⟨g * h⟩
⊢ ((evalAt (g * h)) X) f = ((𝒅ₕ ⋯) ((evalAt h) X)) f

Tactic:
rw [← left_invariant, hfdifferential_apply, hfdifferential_apply, L_mul, fdifferential_comp,
  fdifferential_apply]

Result:
case H
𝕜 : Type u_1
inst✝⁷ : NontriviallyNormedField 𝕜
E : Type u_2
inst✝⁶ : NormedAddCommGroup E
inst✝⁵ : NormedSpace 𝕜 E
H : Type u_3
inst✝⁴ : TopologicalSpace H
I : ModelWithCorners 𝕜 E H
G : Type u_4
inst✝³ : TopologicalSpace G
inst✝² : ChartedSpace H G
inst✝¹ : Monoid G
inst✝ : ContMDiffMul I ∞ G
g h : G
X : LeftInvariantDerivation I G
f : C^∞⟮I, G; 𝕜⟯⟨g * h⟩
⊢ ((𝒅 (𝑳 I g) ((𝑳 I h) 1) ∘ₗ 𝒅 (𝑳 I h) 1) ((evalAt 1) X)) f = ((evalAt h) X) (ContMDiffMap.comp f (𝑳 I g))

Proof state:
case H
𝕜 : Type u_1
inst✝⁷ : NontriviallyNormedField 𝕜
E : Type u_2
inst✝⁶ : NormedAddCommGroup E
inst✝⁵ : NormedSpace 𝕜 E
H : Type u_3
inst✝⁴ : TopologicalSpace H
I : ModelWithCorners 𝕜 E H
G : Type u_4
inst✝³ : TopologicalSpace G
inst✝² : ChartedSpace H G
inst✝¹ : Monoid G
inst✝ : ContMDiffMul I ∞ G
g h : G
X : LeftInvariantDerivation I G
f : C^∞⟮I, G; 𝕜⟯⟨g * h⟩
⊢ ((𝒅 (𝑳 I g) ((𝑳 I h) 1)) ((𝒅 (𝑳 I h) 1) ((evalAt 1) X))) f = ((evalAt h) X) (ContMDiffMap.comp f (𝑳 I g))

Tactic:
erw [fdifferential_apply, ← hfdifferential_apply, left_invariant]

Result:
no goals