@@ -16,9 +16,6 @@ Any partially defined Lipschitz map into `ℓ^∞` can be extended to the whole
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-/
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- set_option autoImplicit true
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-
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-
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noncomputable section
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set_option linter.uppercaseLean3 false
@@ -140,19 +137,19 @@ Theorem 2.2 of [Assaf Naor, *Metric Embeddings and Lipschitz Extensions*][Naor-2
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The same result for the case of a finite type `ι` is implemented in
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`LipschitzOnWith.extend_pi`.
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-/
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- theorem LipschitzOnWith.extend_lp_infty [PseudoMetricSpace α] {s : Set α} {f : α → ℓ^∞(ι)}
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- {K : ℝ≥0 } (hfl : LipschitzOnWith K f s): ∃ g : α → ℓ^∞(ι), LipschitzWith K g ∧ EqOn f g s := by
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+ theorem LipschitzOnWith.extend_lp_infty [PseudoMetricSpace α] {s : Set α} {ι : Type *}
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+ {f : α → ℓ^∞(ι)} {K : ℝ≥0 } (hfl : LipschitzOnWith K f s) :
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+ ∃ g : α → ℓ^∞(ι), LipschitzWith K g ∧ EqOn f g s := by
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-- Construct the coordinate-wise extensions
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rw [LipschitzOnWith.coordinate] at hfl
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- have : ∀ i : ι, ∃ g : α → ℝ, LipschitzWith K g ∧ EqOn (fun x => f x i) g s
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- · intro i
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- exact LipschitzOnWith.extend_real (hfl i) -- use the nonlinear Hahn-Banach theorem here!
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+ have (i: ι) : ∃ g : α → ℝ, LipschitzWith K g ∧ EqOn (fun x => f x i) g s :=
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+ LipschitzOnWith.extend_real (hfl i) -- use the nonlinear Hahn-Banach theorem here!
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choose g hgl hgeq using this
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rcases s.eq_empty_or_nonempty with rfl | ⟨a₀, ha₀_in_s⟩
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· exact ⟨0 , LipschitzWith.const' 0 , by simp⟩
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· -- Show that the extensions are uniformly bounded
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- have hf_extb : ∀ a : α, Memℓp (swap g a) ∞
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- · apply LipschitzWith.uniformly_bounded (swap g) hgl a₀
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+ have hf_extb : ∀ a : α, Memℓp (swap g a) ∞ := by
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+ apply LipschitzWith.uniformly_bounded (swap g) hgl a₀
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use ‖f a₀‖
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rintro - ⟨i, rfl⟩
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simp_rw [← hgeq i ha₀_in_s]
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