Theorem: map_snd_nhdsWithin
File: Mathlib/Topology/Constructions.lean

Proof steps:
state_before: X : Type u
Y : Type v
Z : Type u_1
W : Type u_2
ε : Type u_3
ζ : Type u_4
inst✝⁵ : TopologicalSpace X
inst✝⁴ : TopologicalSpace Y
inst✝³ : TopologicalSpace Z
inst✝² : TopologicalSpace W
inst✝¹ : TopologicalSpace ε
inst✝ : TopologicalSpace ζ
x : X × Y
⊢ map Prod.snd (𝓝[Prod.fst ⁻¹' {x.1}] x) = 𝓝 x.2
state_after: X : Type u
Y : Type v
Z : Type u_1
W : Type u_2
ε : Type u_3
ζ : Type u_4
inst✝⁵ : TopologicalSpace X
inst✝⁴ : TopologicalSpace Y
inst✝³ : TopologicalSpace Z
inst✝² : TopologicalSpace W
inst✝¹ : TopologicalSpace ε
inst✝ : TopologicalSpace ζ
x : X × Y
s : Set Y
hs : s ∈ map Prod.snd (𝓝[Prod.fst ⁻¹' {x.1}] x)
⊢ s ∈ 𝓝 x.2
tactic: refine le_antisymm (continuousAt_snd.mono_left inf_le_left) fun s hs => ?_
state_before: X : Type u
Y : Type v
Z : Type u_1
W : Type u_2
ε : Type u_3
ζ : Type u_4
inst✝⁵ : TopologicalSpace X
inst✝⁴ : TopologicalSpace Y
inst✝³ : TopologicalSpace Z
inst✝² : TopologicalSpace W
inst✝¹ : TopologicalSpace ε
inst✝ : TopologicalSpace ζ
x : X × Y
s : Set Y
hs : s ∈ map Prod.snd (𝓝[Prod.fst ⁻¹' {x.1}] x)
⊢ s ∈ 𝓝 x.2
state_after: case mk
X : Type u
Y : Type v
Z : Type u_1
W : Type u_2
ε : Type u_3
ζ : Type u_4
inst✝⁵ : TopologicalSpace X
inst✝⁴ : TopologicalSpace Y
inst✝³ : TopologicalSpace Z
inst✝² : TopologicalSpace W
inst✝¹ : TopologicalSpace ε
inst✝ : TopologicalSpace ζ
s : Set Y
x : X
y : Y
hs : s ∈ map Prod.snd (𝓝[Prod.fst ⁻¹' {(x, y).1}] (x, y))
⊢ s ∈ 𝓝 (x, y).2
tactic: rcases x with ⟨x, y⟩
state_before: case mk
X : Type u
Y : Type v
Z : Type u_1
W : Type u_2
ε : Type u_3
ζ : Type u_4
inst✝⁵ : TopologicalSpace X
inst✝⁴ : TopologicalSpace Y
inst✝³ : TopologicalSpace Z
inst✝² : TopologicalSpace W
inst✝¹ : TopologicalSpace ε
inst✝ : TopologicalSpace ζ
s : Set Y
x : X
y : Y
hs : s ∈ map Prod.snd (𝓝[Prod.fst ⁻¹' {(x, y).1}] (x, y))
⊢ s ∈ 𝓝 (x, y).2
state_after: case mk
X : Type u
Y : Type v
Z : Type u_1
W : Type u_2
ε : Type u_3
ζ : Type u_4
inst✝⁵ : TopologicalSpace X
inst✝⁴ : TopologicalSpace Y
inst✝³ : TopologicalSpace Z
inst✝² : TopologicalSpace W
inst✝¹ : TopologicalSpace ε
inst✝ : TopologicalSpace ζ
s : Set Y
x : X
y : Y
hs : ∃ u ∈ 𝓝 x, ∃ v ∈ 𝓝 y, u ×ˢ v ⊆ {x_1 | x_1 ∈ Prod.fst ⁻¹' {(x, y).1} → x_1 ∈ Prod.snd ⁻¹' s}
⊢ s ∈ 𝓝 (x, y).2
tactic: rw [mem_map, nhdsWithin, mem_inf_principal, mem_nhds_prod_iff] at hs
state_before: case mk
X : Type u
Y : Type v
Z : Type u_1
W : Type u_2
ε : Type u_3
ζ : Type u_4
inst✝⁵ : TopologicalSpace X
inst✝⁴ : TopologicalSpace Y
inst✝³ : TopologicalSpace Z
inst✝² : TopologicalSpace W
inst✝¹ : TopologicalSpace ε
inst✝ : TopologicalSpace ζ
s : Set Y
x : X
y : Y
hs : ∃ u ∈ 𝓝 x, ∃ v ∈ 𝓝 y, u ×ˢ v ⊆ {x_1 | x_1 ∈ Prod.fst ⁻¹' {(x, y).1} → x_1 ∈ Prod.snd ⁻¹' s}
⊢ s ∈ 𝓝 (x, y).2
state_after: case mk.intro.intro.intro.intro
X : Type u
Y : Type v
Z : Type u_1
W : Type u_2
ε : Type u_3
ζ : Type u_4
inst✝⁵ : TopologicalSpace X
inst✝⁴ : TopologicalSpace Y
inst✝³ : TopologicalSpace Z
inst✝² : TopologicalSpace W
inst✝¹ : TopologicalSpace ε
inst✝ : TopologicalSpace ζ
s : Set Y
x : X
y : Y
u : Set X
hu : u ∈ 𝓝 x
v : Set Y
hv : v ∈ 𝓝 y
H : u ×ˢ v ⊆ {x_1 | x_1 ∈ Prod.fst ⁻¹' {(x, y).1} → x_1 ∈ Prod.snd ⁻¹' s}
⊢ s ∈ 𝓝 (x, y).2
tactic: rcases hs with ⟨u, hu, v, hv, H⟩
state_before: case mk.intro.intro.intro.intro
X : Type u
Y : Type v
Z : Type u_1
W : Type u_2
ε : Type u_3
ζ : Type u_4
inst✝⁵ : TopologicalSpace X
inst✝⁴ : TopologicalSpace Y
inst✝³ : TopologicalSpace Z
inst✝² : TopologicalSpace W
inst✝¹ : TopologicalSpace ε
inst✝ : TopologicalSpace ζ
s : Set Y
x : X
y : Y
u : Set X
hu : u ∈ 𝓝 x
v : Set Y
hv : v ∈ 𝓝 y
H : u ×ˢ v ⊆ {x_1 | x_1 ∈ Prod.fst ⁻¹' {(x, y).1} → x_1 ∈ Prod.snd ⁻¹' s}
⊢ s ∈ 𝓝 (x, y).2
state_after: case mk.intro.intro.intro.intro
X : Type u
Y : Type v
Z : Type u_1
W : Type u_2
ε : Type u_3
ζ : Type u_4
inst✝⁵ : TopologicalSpace X
inst✝⁴ : TopologicalSpace Y
inst✝³ : TopologicalSpace Z
inst✝² : TopologicalSpace W
inst✝¹ : TopologicalSpace ε
inst✝ : TopologicalSpace ζ
s : Set Y
x : X
y : Y
u : Set X
hu : u ∈ 𝓝 x
v : Set Y
hv : v ∈ 𝓝 y
H : ∀ x_1 ∈ u, ∀ y ∈ v, x_1 = x → y ∈ s
⊢ s ∈ 𝓝 (x, y).2
tactic: simp only [prod_subset_iff, mem_singleton_iff, mem_setOf_eq, mem_preimage] at H
state_before: case mk.intro.intro.intro.intro
X : Type u
Y : Type v
Z : Type u_1
W : Type u_2
ε : Type u_3
ζ : Type u_4
inst✝⁵ : TopologicalSpace X
inst✝⁴ : TopologicalSpace Y
inst✝³ : TopologicalSpace Z
inst✝² : TopologicalSpace W
inst✝¹ : TopologicalSpace ε
inst✝ : TopologicalSpace ζ
s : Set Y
x : X
y : Y
u : Set X
hu : u ∈ 𝓝 x
v : Set Y
hv : v ∈ 𝓝 y
H : ∀ x_1 ∈ u, ∀ y ∈ v, x_1 = x → y ∈ s
⊢ s ∈ 𝓝 (x, y).2
state_after: no goals
tactic: exact mem_of_superset hv fun z hz => H _ (mem_of_mem_nhds hu) _ hz rfl