-- Mathlib/Geometry/Manifold/VectorBundle/FiberwiseLinear.lean
theorem source_trans_partialHomeomorph (hU : IsOpen U)
    (hφ : ContinuousOn (fun x => φ x : B → F →L[𝕜] F) U)
    (h2φ : ContinuousOn (fun x => (φ x).symm : B → F →L[𝕜] F) U) (hU' : IsOpen U')
    (hφ' : ContinuousOn (fun x => φ' x : B → F →L[𝕜] F) U')
    (h2φ' : ContinuousOn (fun x => (φ' x).symm : B → F →L[𝕜] F) U') :
    (FiberwiseLinear.partialHomeomorph φ hU hφ h2φ ≫ₕ
          FiberwiseLinear.partialHomeomorph φ' hU' hφ' h2φ').source =
      (U ∩ U') ×ˢ univ

Proof state:
𝕜 : Type u_1
B : Type u_2
F : Type u_3
inst✝³ : TopologicalSpace B
inst✝² : NontriviallyNormedField 𝕜
inst✝¹ : NormedAddCommGroup F
inst✝ : NormedSpace 𝕜 F
φ φ' : B → F ≃L[𝕜] F
U U' : Set B
hU : IsOpen U
hφ : ContinuousOn (fun x => ↑(φ x)) U
h2φ : ContinuousOn (fun x => ↑(φ x).symm) U
hU' : IsOpen U'
hφ' : ContinuousOn (fun x => ↑(φ' x)) U'
h2φ' : ContinuousOn (fun x => ↑(φ' x).symm) U'
⊢ ({ toFun := fun x => (x.1, (φ x.1) x.2), invFun := fun x => (x.1, (φ x.1).symm x.2), source := U ×ˢ univ,
          target := U ×ˢ univ, map_source' := ⋯, map_target' := ⋯, left_inv' := ⋯, right_inv' := ⋯, open_source := ⋯,
          open_target := ⋯, continuousOn_toFun := ⋯, continuousOn_invFun := ⋯ } ≫ₕ
        { toFun := fun x => (x.1, (φ' x.1) x.2), invFun := fun x => (x.1, (φ' x.1).symm x.2), source := U' ×ˢ univ,
          target := U' ×ˢ univ, map_source' := ⋯, map_target' := ⋯, left_inv' := ⋯, right_inv' := ⋯, open_source := ⋯,
          open_target := ⋯, continuousOn_toFun := ⋯, continuousOn_invFun := ⋯ }).source =
    (U ∩ U') ×ˢ univ

Tactic:
mfld_set_tac

Result:
no goals

Proof state:
𝕜 : Type u_1
B : Type u_2
F : Type u_3
inst✝³ : TopologicalSpace B
inst✝² : NontriviallyNormedField 𝕜
inst✝¹ : NormedAddCommGroup F
inst✝ : NormedSpace 𝕜 F
φ φ' : B → F ≃L[𝕜] F
U U' : Set B
hU : IsOpen U
hφ : ContinuousOn (fun x => ↑(φ x)) U
h2φ : ContinuousOn (fun x => ↑(φ x).symm) U
hU' : IsOpen U'
hφ' : ContinuousOn (fun x => ↑(φ' x)) U'
h2φ' : ContinuousOn (fun x => ↑(φ' x).symm) U'
⊢ (partialHomeomorph φ hU hφ h2φ ≫ₕ partialHomeomorph φ' hU' hφ' h2φ').source = (U ∩ U') ×ˢ univ

Tactic:
dsimp only [FiberwiseLinear.partialHomeomorph]

Result:
𝕜 : Type u_1
B : Type u_2
F : Type u_3
inst✝³ : TopologicalSpace B
inst✝² : NontriviallyNormedField 𝕜
inst✝¹ : NormedAddCommGroup F
inst✝ : NormedSpace 𝕜 F
φ φ' : B → F ≃L[𝕜] F
U U' : Set B
hU : IsOpen U
hφ : ContinuousOn (fun x => ↑(φ x)) U
h2φ : ContinuousOn (fun x => ↑(φ x).symm) U
hU' : IsOpen U'
hφ' : ContinuousOn (fun x => ↑(φ' x)) U'
h2φ' : ContinuousOn (fun x => ↑(φ' x).symm) U'
⊢ ({ toFun := fun x => (x.1, (φ x.1) x.2), invFun := fun x => (x.1, (φ x.1).symm x.2), source := U ×ˢ univ,
          target := U ×ˢ univ, map_source' := ⋯, map_target' := ⋯, left_inv' := ⋯, right_inv' := ⋯, open_source := ⋯,
          open_target := ⋯, continuousOn_toFun := ⋯, continuousOn_invFun := ⋯ } ≫ₕ
        { toFun := fun x => (x.1, (φ' x.1) x.2), invFun := fun x => (x.1, (φ' x.1).symm x.2), source := U' ×ˢ univ,
          target := U' ×ˢ univ, map_source' := ⋯, map_target' := ⋯, left_inv' := ⋯, right_inv' := ⋯, open_source := ⋯,
          open_target := ⋯, continuousOn_toFun := ⋯, continuousOn_invFun := ⋯ }).source =
    (U ∩ U') ×ˢ univ