-- Mathlib/Geometry/Manifold/VectorBundle/Basic.lean
theorem contMDiff_zeroSection : ContMDiff IB (IB.prod 𝓘(𝕜, F)) n (zeroSection F E) := fun x ↦ by
  unfold zeroSection
  rw [Bundle.contMDiffAt_section]
  apply (contMDiffAt_const (c := 0)).congr_of_eventuallyEq
  filter_upwards [(trivializationAt F E x).open_baseSet.mem_nhds
    (mem_baseSet_trivializationAt F E x)] with y hy
    using congr_arg Prod.snd <| (trivializationAt F E x).zeroSection 𝕜 hy

Proof state:
n : WithTop ℕ∞
𝕜 : Type u_1
B : Type u_2
F : Type u_4
E : B → Type u_6
inst✝¹³ : NontriviallyNormedField 𝕜
inst✝¹² : NormedAddCommGroup F
inst✝¹¹ : NormedSpace 𝕜 F
inst✝¹⁰ : TopologicalSpace (TotalSpace F E)
inst✝⁹ : (x : B) → TopologicalSpace (E x)
EB : Type u_7
inst✝⁸ : NormedAddCommGroup EB
inst✝⁷ : NormedSpace 𝕜 EB
HB : Type u_8
inst✝⁶ : TopologicalSpace HB
IB : ModelWithCorners 𝕜 EB HB
inst✝⁵ : TopologicalSpace B
inst✝⁴ : ChartedSpace HB B
inst✝³ : FiberBundle F E
inst✝² : (x : B) → AddCommMonoid (E x)
inst✝¹ : (x : B) → Module 𝕜 (E x)
inst✝ : VectorBundle 𝕜 F E
x : B
⊢ ContMDiffAt IB (IB.prod 𝓘(𝕜, F)) n (zeroSection F E) x

Tactic:
unfold zeroSection

Result:
n : WithTop ℕ∞
𝕜 : Type u_1
B : Type u_2
F : Type u_4
E : B → Type u_6
inst✝¹³ : NontriviallyNormedField 𝕜
inst✝¹² : NormedAddCommGroup F
inst✝¹¹ : NormedSpace 𝕜 F
inst✝¹⁰ : TopologicalSpace (TotalSpace F E)
inst✝⁹ : (x : B) → TopologicalSpace (E x)
EB : Type u_7
inst✝⁸ : NormedAddCommGroup EB
inst✝⁷ : NormedSpace 𝕜 EB
HB : Type u_8
inst✝⁶ : TopologicalSpace HB
IB : ModelWithCorners 𝕜 EB HB
inst✝⁵ : TopologicalSpace B
inst✝⁴ : ChartedSpace HB B
inst✝³ : FiberBundle F E
inst✝² : (x : B) → AddCommMonoid (E x)
inst✝¹ : (x : B) → Module 𝕜 (E x)
inst✝ : VectorBundle 𝕜 F E
x : B
⊢ ContMDiffAt IB (IB.prod 𝓘(𝕜, F)) n (fun x => { proj := x, snd := 0 }) x

Proof state:
n : WithTop ℕ∞
𝕜 : Type u_1
B : Type u_2
F : Type u_4
E : B → Type u_6
inst✝¹³ : NontriviallyNormedField 𝕜
inst✝¹² : NormedAddCommGroup F
inst✝¹¹ : NormedSpace 𝕜 F
inst✝¹⁰ : TopologicalSpace (TotalSpace F E)
inst✝⁹ : (x : B) → TopologicalSpace (E x)
EB : Type u_7
inst✝⁸ : NormedAddCommGroup EB
inst✝⁷ : NormedSpace 𝕜 EB
HB : Type u_8
inst✝⁶ : TopologicalSpace HB
IB : ModelWithCorners 𝕜 EB HB
inst✝⁵ : TopologicalSpace B
inst✝⁴ : ChartedSpace HB B
inst✝³ : FiberBundle F E
inst✝² : (x : B) → AddCommMonoid (E x)
inst✝¹ : (x : B) → Module 𝕜 (E x)
inst✝ : VectorBundle 𝕜 F E
x : B
⊢ (fun x_1 => (↑(trivializationAt F E x) { proj := x_1, snd := 0 }).2) =ᶠ[𝓝 x] fun x => 0

Tactic:
filter_upwards [(trivializationAt F E x).open_baseSet.mem_nhds
  (mem_baseSet_trivializationAt F E x)] with y hy
  using congr_arg Prod.snd <| (trivializationAt F E x).zeroSection 𝕜 hy

Result:
no goals

Proof state:
n : WithTop ℕ∞
𝕜 : Type u_1
B : Type u_2
F : Type u_4
E : B → Type u_6
inst✝¹³ : NontriviallyNormedField 𝕜
inst✝¹² : NormedAddCommGroup F
inst✝¹¹ : NormedSpace 𝕜 F
inst✝¹⁰ : TopologicalSpace (TotalSpace F E)
inst✝⁹ : (x : B) → TopologicalSpace (E x)
EB : Type u_7
inst✝⁸ : NormedAddCommGroup EB
inst✝⁷ : NormedSpace 𝕜 EB
HB : Type u_8
inst✝⁶ : TopologicalSpace HB
IB : ModelWithCorners 𝕜 EB HB
inst✝⁵ : TopologicalSpace B
inst✝⁴ : ChartedSpace HB B
inst✝³ : FiberBundle F E
inst✝² : (x : B) → AddCommMonoid (E x)
inst✝¹ : (x : B) → Module 𝕜 (E x)
inst✝ : VectorBundle 𝕜 F E
x : B
⊢ ContMDiffAt IB 𝓘(𝕜, F) n (fun x_1 => (↑(trivializationAt F E x) { proj := x_1, snd := 0 }).2) x

Tactic:
apply (contMDiffAt_const (c := 0)).congr_of_eventuallyEq

Result:
n : WithTop ℕ∞
𝕜 : Type u_1
B : Type u_2
F : Type u_4
E : B → Type u_6
inst✝¹³ : NontriviallyNormedField 𝕜
inst✝¹² : NormedAddCommGroup F
inst✝¹¹ : NormedSpace 𝕜 F
inst✝¹⁰ : TopologicalSpace (TotalSpace F E)
inst✝⁹ : (x : B) → TopologicalSpace (E x)
EB : Type u_7
inst✝⁸ : NormedAddCommGroup EB
inst✝⁷ : NormedSpace 𝕜 EB
HB : Type u_8
inst✝⁶ : TopologicalSpace HB
IB : ModelWithCorners 𝕜 EB HB
inst✝⁵ : TopologicalSpace B
inst✝⁴ : ChartedSpace HB B
inst✝³ : FiberBundle F E
inst✝² : (x : B) → AddCommMonoid (E x)
inst✝¹ : (x : B) → Module 𝕜 (E x)
inst✝ : VectorBundle 𝕜 F E
x : B
⊢ (fun x_1 => (↑(trivializationAt F E x) { proj := x_1, snd := 0 }).2) =ᶠ[𝓝 x] fun x => 0

Proof state:
n : WithTop ℕ∞
𝕜 : Type u_1
B : Type u_2
F : Type u_4
E : B → Type u_6
inst✝¹³ : NontriviallyNormedField 𝕜
inst✝¹² : NormedAddCommGroup F
inst✝¹¹ : NormedSpace 𝕜 F
inst✝¹⁰ : TopologicalSpace (TotalSpace F E)
inst✝⁹ : (x : B) → TopologicalSpace (E x)
EB : Type u_7
inst✝⁸ : NormedAddCommGroup EB
inst✝⁷ : NormedSpace 𝕜 EB
HB : Type u_8
inst✝⁶ : TopologicalSpace HB
IB : ModelWithCorners 𝕜 EB HB
inst✝⁵ : TopologicalSpace B
inst✝⁴ : ChartedSpace HB B
inst✝³ : FiberBundle F E
inst✝² : (x : B) → AddCommMonoid (E x)
inst✝¹ : (x : B) → Module 𝕜 (E x)
inst✝ : VectorBundle 𝕜 F E
x : B
⊢ ContMDiffAt IB (IB.prod 𝓘(𝕜, F)) n (fun x => { proj := x, snd := 0 }) x

Tactic:
rw [Bundle.contMDiffAt_section]

Result:
n : WithTop ℕ∞
𝕜 : Type u_1
B : Type u_2
F : Type u_4
E : B → Type u_6
inst✝¹³ : NontriviallyNormedField 𝕜
inst✝¹² : NormedAddCommGroup F
inst✝¹¹ : NormedSpace 𝕜 F
inst✝¹⁰ : TopologicalSpace (TotalSpace F E)
inst✝⁹ : (x : B) → TopologicalSpace (E x)
EB : Type u_7
inst✝⁸ : NormedAddCommGroup EB
inst✝⁷ : NormedSpace 𝕜 EB
HB : Type u_8
inst✝⁶ : TopologicalSpace HB
IB : ModelWithCorners 𝕜 EB HB
inst✝⁵ : TopologicalSpace B
inst✝⁴ : ChartedSpace HB B
inst✝³ : FiberBundle F E
inst✝² : (x : B) → AddCommMonoid (E x)
inst✝¹ : (x : B) → Module 𝕜 (E x)
inst✝ : VectorBundle 𝕜 F E
x : B
⊢ ContMDiffAt IB 𝓘(𝕜, F) n (fun x_1 => (↑(trivializationAt F E x) { proj := x_1, snd := 0 }).2) x