Theorem: LinearMap.tendsto_birkhoffAverage_of_ker_subset_closure
File: Mathlib/Analysis/InnerProductSpace/MeanErgodic.lean

Proof steps:
state_before: 𝕜 : Type u_1
E : Type u_2
inst✝² : RCLike 𝕜
inst✝¹ : NormedAddCommGroup E
inst✝ : NormedSpace 𝕜 E
f : E →ₗ[𝕜] E
hf : LipschitzWith 1 ⇑f
g : E →L[𝕜] ↥(eqLocus f 1)
hg_proj : ∀ (x : ↥(eqLocus f 1)), g ↑x = x
hg_ker : ↑(ker g) ⊆ closure ↑(range (f - 1))
x : E
⊢ Tendsto (fun x_1 => birkhoffAverage 𝕜 (⇑f) _root_.id x_1 x) atTop (𝓝 ↑(g x))
state_after: case intro.intro.intro.intro
𝕜 : Type u_1
E : Type u_2
inst✝² : RCLike 𝕜
inst✝¹ : NormedAddCommGroup E
inst✝ : NormedSpace 𝕜 E
f : E →ₗ[𝕜] E
hf : LipschitzWith 1 ⇑f
g : E →L[𝕜] ↥(eqLocus f 1)
hg_proj : ∀ (x : ↥(eqLocus f 1)), g ↑x = x
hg_ker : ↑(ker g) ⊆ closure ↑(range (f - 1))
y : E
hy : g y = 0
z : E
hz : IsFixedPt (⇑f) z
⊢ Tendsto (fun x => birkhoffAverage 𝕜 (⇑f) _root_.id x (y + z)) atTop (𝓝 ↑(g (y + z)))
tactic: obtain ⟨y, hy, z, hz, rfl⟩ : ∃ y, g y = 0 ∧ ∃ z, IsFixedPt f z ∧ x = y + z :=
    ⟨x - g x, by simp [hg_proj], g x, (g x).2, by simp⟩
state_before: case intro.intro.intro.intro
𝕜 : Type u_1
E : Type u_2
inst✝² : RCLike 𝕜
inst✝¹ : NormedAddCommGroup E
inst✝ : NormedSpace 𝕜 E
f : E →ₗ[𝕜] E
hf : LipschitzWith 1 ⇑f
g : E →L[𝕜] ↥(eqLocus f 1)
hg_proj : ∀ (x : ↥(eqLocus f 1)), g ↑x = x
hg_ker : ↑(ker g) ⊆ closure ↑(range (f - 1))
y : E
hy : g y = 0
z : E
hz : IsFixedPt (⇑f) z
this : IsClosed {x | Tendsto (fun x_1 => birkhoffAverage 𝕜 (⇑f) _root_.id x_1 x) atTop (𝓝 0)}
⊢ Tendsto (fun x => birkhoffAverage 𝕜 (⇑f) _root_.id x y) atTop (𝓝 0)
state_after: case intro.intro.intro.intro
𝕜 : Type u_1
E : Type u_2
inst✝² : RCLike 𝕜
inst✝¹ : NormedAddCommGroup E
inst✝ : NormedSpace 𝕜 E
f : E →ₗ[𝕜] E
hf : LipschitzWith 1 ⇑f
g : E →L[𝕜] ↥(eqLocus f 1)
hg_proj : ∀ (x : ↥(eqLocus f 1)), g ↑x = x
hg_ker : ↑(ker g) ⊆ closure ↑(range (f - 1))
y : E
hy : g y = 0
z : E
hz : IsFixedPt (⇑f) z
this : IsClosed {x | Tendsto (fun x_1 => birkhoffAverage 𝕜 (⇑f) _root_.id x_1 x) atTop (𝓝 0)}
x : E
⊢ (f - 1) x ∈ {x | Tendsto (fun x_1 => birkhoffAverage 𝕜 (⇑f) _root_.id x_1 x) atTop (𝓝 0)}
tactic: refine closure_minimal (Set.forall_mem_range.2 fun x ↦ ?_) this (hg_ker hy)
state_before: case intro.intro.intro.intro
𝕜 : Type u_1
E : Type u_2
inst✝² : RCLike 𝕜
inst✝¹ : NormedAddCommGroup E
inst✝ : NormedSpace 𝕜 E
f : E →ₗ[𝕜] E
hf : LipschitzWith 1 ⇑f
g : E →L[𝕜] ↥(eqLocus f 1)
hg_proj : ∀ (x : ↥(eqLocus f 1)), g ↑x = x
hg_ker : ↑(ker g) ⊆ closure ↑(range (f - 1))
y : E
hy : g y = 0
z : E
hz : IsFixedPt (⇑f) z
this✝ : IsClosed {x | Tendsto (fun x_1 => birkhoffAverage 𝕜 (⇑f) _root_.id x_1 x) atTop (𝓝 0)}
x : E
this : Bornology.IsBounded (Set.range fun x_1 => _root_.id ((⇑f)^[x_1] x))
⊢ (f - 1) x ∈ {x | Tendsto (fun x_1 => birkhoffAverage 𝕜 (⇑f) _root_.id x_1 x) atTop (𝓝 0)}
state_after: case intro.intro.intro.intro
𝕜 : Type u_1
E : Type u_2
inst✝² : RCLike 𝕜
inst✝¹ : NormedAddCommGroup E
inst✝ : NormedSpace 𝕜 E
f : E →ₗ[𝕜] E
hf : LipschitzWith 1 ⇑f
g : E →L[𝕜] ↥(eqLocus f 1)
hg_proj : ∀ (x : ↥(eqLocus f 1)), g ↑x = x
hg_ker : ↑(ker g) ⊆ closure ↑(range (f - 1))
y : E
hy : g y = 0
z : E
hz : IsFixedPt (⇑f) z
this✝ : IsClosed {x | Tendsto (fun x_1 => birkhoffAverage 𝕜 (⇑f) _root_.id x_1 x) atTop (𝓝 0)}
x : E
this : Bornology.IsBounded (Set.range fun x_1 => _root_.id ((⇑f)^[x_1] x))
H : ∀ (n : ℕ) (x y : E), (⇑f)^[n] (x - y) = (⇑f)^[n] x - (⇑f)^[n] y
⊢ (f - 1) x ∈ {x | Tendsto (fun x_1 => birkhoffAverage 𝕜 (⇑f) _root_.id x_1 x) atTop (𝓝 0)}
tactic: have H : ∀ n x y, f^[n] (x - y) = f^[n] x - f^[n] y := iterate_map_sub (f : E →+ E)
state_before: case intro.intro.intro.intro
𝕜 : Type u_1
E : Type u_2
inst✝² : RCLike 𝕜
inst✝¹ : NormedAddCommGroup E
inst✝ : NormedSpace 𝕜 E
f : E →ₗ[𝕜] E
hf : LipschitzWith 1 ⇑f
g : E →L[𝕜] ↥(eqLocus f 1)
hg_proj : ∀ (x : ↥(eqLocus f 1)), g ↑x = x
hg_ker : ↑(ker g) ⊆ closure ↑(range (f - 1))
y : E
hy : g y = 0
z : E
hz : IsFixedPt (⇑f) z
this✝ : IsClosed {x | Tendsto (fun x_1 => birkhoffAverage 𝕜 (⇑f) _root_.id x_1 x) atTop (𝓝 0)}
x : E
this : Bornology.IsBounded (Set.range fun x_1 => _root_.id ((⇑f)^[x_1] x))
H : ∀ (n : ℕ) (x y : E), (⇑f)^[n] (x - y) = (⇑f)^[n] x - (⇑f)^[n] y
⊢ (f - 1) x ∈ {x | Tendsto (fun x_1 => birkhoffAverage 𝕜 (⇑f) _root_.id x_1 x) atTop (𝓝 0)}
state_after: no goals
tactic: simpa [birkhoffAverage, birkhoffSum, Finset.sum_sub_distrib, smul_sub, H]
    using tendsto_birkhoffAverage_apply_sub_birkhoffAverage 𝕜 this