-- Mathlib/MeasureTheory/Integral/RieszMarkovKakutani/Basic.lean
theorem rieszContentAux_image_nonempty (K : Compacts X) :
    (Λ '' { f : C_c(X, ℝ≥0) | ∀ x ∈ K, (1 : ℝ≥0) ≤ f x }).Nonempty

Proof state:
X : Type u_1
inst✝² : TopologicalSpace X
Λ : (X →C_c ℝ≥0) →ₗ[ℝ≥0] ℝ≥0
inst✝¹ : T2Space X
inst✝ : LocallyCompactSpace X
K : Compacts X
⊢ {f | ∀ x ∈ K, 1 ≤ f x}.Nonempty

Tactic:
obtain ⟨V, hVcp, hKsubintV⟩ := exists_compact_superset K.2

Result:
case intro.intro
X : Type u_1
inst✝² : TopologicalSpace X
Λ : (X →C_c ℝ≥0) →ₗ[ℝ≥0] ℝ≥0
inst✝¹ : T2Space X
inst✝ : LocallyCompactSpace X
K : Compacts X
V : Set X
hVcp : IsCompact V
hKsubintV : K.carrier ⊆ interior V
⊢ {f | ∀ x ∈ K, 1 ≤ f x}.Nonempty

Proof state:
case h.hab
X : Type u_1
inst✝² : TopologicalSpace X
Λ : (X →C_c ℝ≥0) →ₗ[ℝ≥0] ℝ≥0
inst✝¹ : T2Space X
inst✝ : LocallyCompactSpace X
K : Compacts X
V : Set X
hVcp : IsCompact V
hKsubintV : K.carrier ⊆ interior V
hIsCompact_closure_interior : IsCompact (closure (interior V))
f : C(X, ℝ)
hsuppfsubV : tsupport ⇑f ⊆ interior V
hfeq1onK : EqOn (⇑f) 1 K.carrier
hfinicc : ∀ (x : X), f x ∈ Icc 0 1
hfHasCompactSupport : HasCompactSupport ⇑f
x : X
hx : x ∈ K
⊢ 1 = f x

Tactic:
exact hfeq1onK.symm hx

Result:
no goals

Proof state:
X : Type u_1
inst✝² : TopologicalSpace X
Λ : (X →C_c ℝ≥0) →ₗ[ℝ≥0] ℝ≥0
inst✝¹ : T2Space X
inst✝ : LocallyCompactSpace X
K : Compacts X
⊢ (⇑Λ '' {f | ∀ x ∈ K, 1 ≤ f x}).Nonempty

Tactic:
rw [image_nonempty]

Result:
X : Type u_1
inst✝² : TopologicalSpace X
Λ : (X →C_c ℝ≥0) →ₗ[ℝ≥0] ℝ≥0
inst✝¹ : T2Space X
inst✝ : LocallyCompactSpace X
K : Compacts X
⊢ {f | ∀ x ∈ K, 1 ≤ f x}.Nonempty

Proof state:
case h
X : Type u_1
inst✝² : TopologicalSpace X
Λ : (X →C_c ℝ≥0) →ₗ[ℝ≥0] ℝ≥0
inst✝¹ : T2Space X
inst✝ : LocallyCompactSpace X
K : Compacts X
V : Set X
hVcp : IsCompact V
hKsubintV : K.carrier ⊆ interior V
hIsCompact_closure_interior : IsCompact (closure (interior V))
f : C(X, ℝ)
hsuppfsubV : tsupport ⇑f ⊆ interior V
hfeq1onK : EqOn (⇑f) 1 K.carrier
hfinicc : ∀ (x : X), f x ∈ Icc 0 1
hfHasCompactSupport : HasCompactSupport ⇑f
x : X
hx : x ∈ K
⊢ 1 ≤ { toContinuousMap := f, hasCompactSupport' := hfHasCompactSupport }.nnrealPart x

Tactic:
apply le_of_eq

Result:
case h.hab
X : Type u_1
inst✝² : TopologicalSpace X
Λ : (X →C_c ℝ≥0) →ₗ[ℝ≥0] ℝ≥0
inst✝¹ : T2Space X
inst✝ : LocallyCompactSpace X
K : Compacts X
V : Set X
hVcp : IsCompact V
hKsubintV : K.carrier ⊆ interior V
hIsCompact_closure_interior : IsCompact (closure (interior V))
f : C(X, ℝ)
hsuppfsubV : tsupport ⇑f ⊆ interior V
hfeq1onK : EqOn (⇑f) 1 K.carrier
hfinicc : ∀ (x : X), f x ∈ Icc 0 1
hfHasCompactSupport : HasCompactSupport ⇑f
x : X
hx : x ∈ K
⊢ 1 = { toContinuousMap := f, hasCompactSupport' := hfHasCompactSupport }.nnrealPart x

Proof state:
case intro.intro
X : Type u_1
inst✝² : TopologicalSpace X
Λ : (X →C_c ℝ≥0) →ₗ[ℝ≥0] ℝ≥0
inst✝¹ : T2Space X
inst✝ : LocallyCompactSpace X
K : Compacts X
V : Set X
hVcp : IsCompact V
hKsubintV : K.carrier ⊆ interior V
hIsCompact_closure_interior : IsCompact (closure (interior V))
⊢ {f | ∀ x ∈ K, 1 ≤ f x}.Nonempty

Tactic:
obtain ⟨f, hsuppfsubV, hfeq1onK, hfinicc⟩ :=
  exists_tsupport_one_of_isOpen_isClosed isOpen_interior hIsCompact_closure_interior
    (IsCompact.isClosed K.2) hKsubintV

Result:
case intro.intro.intro.intro.intro
X : Type u_1
inst✝² : TopologicalSpace X
Λ : (X →C_c ℝ≥0) →ₗ[ℝ≥0] ℝ≥0
inst✝¹ : T2Space X
inst✝ : LocallyCompactSpace X
K : Compacts X
V : Set X
hVcp : IsCompact V
hKsubintV : K.carrier ⊆ interior V
hIsCompact_closure_interior : IsCompact (closure (interior V))
f : C(X, ℝ)
hsuppfsubV : tsupport ⇑f ⊆ interior V
hfeq1onK : EqOn (⇑f) 1 K.carrier
hfinicc : ∀ (x : X), f x ∈ Icc 0 1
⊢ {f | ∀ x ∈ K, 1 ≤ f x}.Nonempty