Module: Mathlib.Analysis.Calculus.ContDiff.Comp

Goal state before:
pp: case refine_2
𝕜 : Type u_1
E : Type u_2
F : Type u_3
G : Type u_4
inst✝⁶ : NontriviallyNormedField 𝕜
inst✝⁵ : NormedAddCommGroup E
inst✝⁴ : NormedSpace 𝕜 E
inst✝³ : NormedAddCommGroup F
inst✝² : NormedSpace 𝕜 F
inst✝¹ : NormedAddCommGroup G
inst✝ : NormedSpace 𝕜 G
s : Set E
n : ℕ∞ω
f : E → F → G
g : E → F
t : Set F
hn : n ≠ ∞
x₀ : E
hf : ContDiffWithinAt 𝕜 (n + 1) (uncurry f) (insert x₀ s ×ˢ t) (x₀, g x₀)
hg : ContDiffWithinAt 𝕜 n g s x₀
hgt : t ∈ 𝓝[g '' s] g x₀
hst : insert x₀ s ×ˢ t ∈ 𝓝[(fun x ↦ (x, g x)) '' s] (x₀, g x₀)
v : Set (E × F)
hv : v ∈ 𝓝[insert (x₀, g x₀) (insert x₀ s ×ˢ t)] (x₀, g x₀)
hvs : v ⊆ insert (x₀, g x₀) (insert x₀ s ×ˢ t)
f_an : n = ω → AnalyticOn 𝕜 (uncurry f) v
f' : E × F → E × F →L[𝕜] G
hvf' : ∀ x ∈ v, HasFDerivWithinAt (uncurry f) (f' x) (insert x₀ s ×ˢ t) x
hf' : ContDiffWithinAt 𝕜 n f' (insert x₀ s ×ˢ t) (x₀, g x₀)
⊢ ∀ x ∈ (fun z ↦ (z, g z)) ⁻¹' v ∩ insert x₀ s,
    HasFDerivWithinAt (f x) ((fun z ↦ f' (z, g z) ∘SL ContinuousLinearMap.inr 𝕜 E F) x) t (g x)

pp: case refine_3
𝕜 : Type u_1
E : Type u_2
F : Type u_3
G : Type u_4
inst✝⁶ : NontriviallyNormedField 𝕜
inst✝⁵ : NormedAddCommGroup E
inst✝⁴ : NormedSpace 𝕜 E
inst✝³ : NormedAddCommGroup F
inst✝² : NormedSpace 𝕜 F
inst✝¹ : NormedAddCommGroup G
inst✝ : NormedSpace 𝕜 G
s : Set E
n : ℕ∞ω
f : E → F → G
g : E → F
t : Set F
hn : n ≠ ∞
x₀ : E
hf : ContDiffWithinAt 𝕜 (n + 1) (uncurry f) (insert x₀ s ×ˢ t) (x₀, g x₀)
hg : ContDiffWithinAt 𝕜 n g s x₀
hgt : t ∈ 𝓝[g '' s] g x₀
hst : insert x₀ s ×ˢ t ∈ 𝓝[(fun x ↦ (x, g x)) '' s] (x₀, g x₀)
v : Set (E × F)
hv : v ∈ 𝓝[insert (x₀, g x₀) (insert x₀ s ×ˢ t)] (x₀, g x₀)
hvs : v ⊆ insert (x₀, g x₀) (insert x₀ s ×ˢ t)
f_an : n = ω → AnalyticOn 𝕜 (uncurry f) v
f' : E × F → E × F →L[𝕜] G
hvf' : ∀ x ∈ v, HasFDerivWithinAt (uncurry f) (f' x) (insert x₀ s ×ˢ t) x
hf' : ContDiffWithinAt 𝕜 n f' (insert x₀ s ×ˢ t) (x₀, g x₀)
⊢ ContDiffWithinAt 𝕜 n (fun x ↦ (fun z ↦ f' (z, g z) ∘SL ContinuousLinearMap.inr 𝕜 E F) x) s x₀

Tactic:
· intro z hz
    have := hvf' (z, g z) hz.1
    refine this.comp _ (hasFDerivAt_prodMk_right _ _).hasFDerivWithinAt ?_
    exact mapsTo_iff_image_subset.mpr (image_prodMk_subset_prod_right hz.2)

Goal state after:
case refine_3
𝕜 : Type u_1
E : Type u_2
F : Type u_3
G : Type u_4
inst✝⁶ : NontriviallyNormedField 𝕜
inst✝⁵ : NormedAddCommGroup E
inst✝⁴ : NormedSpace 𝕜 E
inst✝³ : NormedAddCommGroup F
inst✝² : NormedSpace 𝕜 F
inst✝¹ : NormedAddCommGroup G
inst✝ : NormedSpace 𝕜 G
s : Set E
n : ℕ∞ω
f : E → F → G
g : E → F
t : Set F
hn : n ≠ ∞
x₀ : E
hf : ContDiffWithinAt 𝕜 (n + 1) (uncurry f) (insert x₀ s ×ˢ t) (x₀, g x₀)
hg : ContDiffWithinAt 𝕜 n g s x₀
hgt : t ∈ 𝓝[g '' s] g x₀
hst : insert x₀ s ×ˢ t ∈ 𝓝[(fun x ↦ (x, g x)) '' s] (x₀, g x₀)
v : Set (E × F)
hv : v ∈ 𝓝[insert (x₀, g x₀) (insert x₀ s ×ˢ t)] (x₀, g x₀)
hvs : v ⊆ insert (x₀, g x₀) (insert x₀ s ×ˢ t)
f_an : n = ω → AnalyticOn 𝕜 (uncurry f) v
f' : E × F → E × F →L[𝕜] G
hvf' : ∀ x ∈ v, HasFDerivWithinAt (uncurry f) (f' x) (insert x₀ s ×ˢ t) x
hf' : ContDiffWithinAt 𝕜 n f' (insert x₀ s ×ˢ t) (x₀, g x₀)
⊢ ContDiffWithinAt 𝕜 n (fun x ↦ (fun z ↦ f' (z, g z) ∘SL ContinuousLinearMap.inr 𝕜 E F) x) s x₀