-- Mathlib/Geometry/Manifold/IsManifold/InteriorBoundary.lean
/-- The interior of `M × N` is the product of the interiors of `M` and `N`. -/
lemma interior_prod :
    (I.prod J).interior (M × N) = (I.interior M) ×ˢ (J.interior N)

Proof state:
case h
𝕜 : Type u_1
inst✝¹⁰ : NontriviallyNormedField 𝕜
E : Type u_2
inst✝⁹ : NormedAddCommGroup E
inst✝⁸ : NormedSpace 𝕜 E
H : Type u_3
inst✝⁷ : TopologicalSpace H
I : ModelWithCorners 𝕜 E H
M : Type u_4
inst✝⁶ : TopologicalSpace M
inst✝⁵ : ChartedSpace H M
E' : Type u_5
inst✝⁴ : NormedAddCommGroup E'
inst✝³ : NormedSpace 𝕜 E'
H' : Type u_6
inst✝² : TopologicalSpace H'
N : Type u_7
inst✝¹ : TopologicalSpace N
inst✝ : ChartedSpace H' N
J : ModelWithCorners 𝕜 E' H'
p : M × N
aux : interior (range ↑I) ×ˢ interior (range ↑J) = interior (range ↑(I.prod J))
⊢ p ∈ ModelWithCorners.interior (M × N) ↔ p ∈ ModelWithCorners.interior M ×ˢ ModelWithCorners.interior N

Tactic:
constructor <;> intro hp

Result:
case h.mp
𝕜 : Type u_1
inst✝¹⁰ : NontriviallyNormedField 𝕜
E : Type u_2
inst✝⁹ : NormedAddCommGroup E
inst✝⁸ : NormedSpace 𝕜 E
H : Type u_3
inst✝⁷ : TopologicalSpace H
I : ModelWithCorners 𝕜 E H
M : Type u_4
inst✝⁶ : TopologicalSpace M
inst✝⁵ : ChartedSpace H M
E' : Type u_5
inst✝⁴ : NormedAddCommGroup E'
inst✝³ : NormedSpace 𝕜 E'
H' : Type u_6
inst✝² : TopologicalSpace H'
N : Type u_7
inst✝¹ : TopologicalSpace N
inst✝ : ChartedSpace H' N
J : ModelWithCorners 𝕜 E' H'
p : M × N
aux : interior (range ↑I) ×ˢ interior (range ↑J) = interior (range ↑(I.prod J))
hp : p ∈ ModelWithCorners.interior (M × N)
⊢ p ∈ ModelWithCorners.interior M ×ˢ ModelWithCorners.interior N

case h.mpr
𝕜 : Type u_1
inst✝¹⁰ : NontriviallyNormedField 𝕜
E : Type u_2
inst✝⁹ : NormedAddCommGroup E
inst✝⁸ : NormedSpace 𝕜 E
H : Type u_3
inst✝⁷ : TopologicalSpace H
I : ModelWithCorners 𝕜 E H
M : Type u_4
inst✝⁶ : TopologicalSpace M
inst✝⁵ : ChartedSpace H M
E' : Type u_5
inst✝⁴ : NormedAddCommGroup E'
inst✝³ : NormedSpace 𝕜 E'
H' : Type u_6
inst✝² : TopologicalSpace H'
N : Type u_7
inst✝¹ : TopologicalSpace N
inst✝ : ChartedSpace H' N
J : ModelWithCorners 𝕜 E' H'
p : M × N
aux : interior (range ↑I) ×ˢ interior (range ↑J) = interior (range ↑(I.prod J))
hp : p ∈ ModelWithCorners.interior M ×ˢ ModelWithCorners.interior N
⊢ p ∈ ModelWithCorners.interior (M × N)

Proof state:
case h
𝕜 : Type u_1
inst✝¹⁰ : NontriviallyNormedField 𝕜
E : Type u_2
inst✝⁹ : NormedAddCommGroup E
inst✝⁸ : NormedSpace 𝕜 E
H : Type u_3
inst✝⁷ : TopologicalSpace H
I : ModelWithCorners 𝕜 E H
M : Type u_4
inst✝⁶ : TopologicalSpace M
inst✝⁵ : ChartedSpace H M
E' : Type u_5
inst✝⁴ : NormedAddCommGroup E'
inst✝³ : NormedSpace 𝕜 E'
H' : Type u_6
inst✝² : TopologicalSpace H'
N : Type u_7
inst✝¹ : TopologicalSpace N
inst✝ : ChartedSpace H' N
J : ModelWithCorners 𝕜 E' H'
p : M × N
⊢ p ∈ ModelWithCorners.interior (M × N) ↔ p ∈ ModelWithCorners.interior M ×ˢ ModelWithCorners.interior N

Tactic:
have aux : (interior (range ↑I)) ×ˢ (interior (range J)) = interior (range (I.prod J)) := by
  rw [← interior_prod_eq, ← Set.range_prod_map, modelWithCorners_prod_coe]

Result:
case h
𝕜 : Type u_1
inst✝¹⁰ : NontriviallyNormedField 𝕜
E : Type u_2
inst✝⁹ : NormedAddCommGroup E
inst✝⁸ : NormedSpace 𝕜 E
H : Type u_3
inst✝⁷ : TopologicalSpace H
I : ModelWithCorners 𝕜 E H
M : Type u_4
inst✝⁶ : TopologicalSpace M
inst✝⁵ : ChartedSpace H M
E' : Type u_5
inst✝⁴ : NormedAddCommGroup E'
inst✝³ : NormedSpace 𝕜 E'
H' : Type u_6
inst✝² : TopologicalSpace H'
N : Type u_7
inst✝¹ : TopologicalSpace N
inst✝ : ChartedSpace H' N
J : ModelWithCorners 𝕜 E' H'
p : M × N
aux : interior (range ↑I) ×ˢ interior (range ↑J) = interior (range ↑(I.prod J))
⊢ p ∈ ModelWithCorners.interior (M × N) ↔ p ∈ ModelWithCorners.interior M ×ˢ ModelWithCorners.interior N

Proof state:
case h.mpr
𝕜 : Type u_1
inst✝¹⁰ : NontriviallyNormedField 𝕜
E : Type u_2
inst✝⁹ : NormedAddCommGroup E
inst✝⁸ : NormedSpace 𝕜 E
H : Type u_3
inst✝⁷ : TopologicalSpace H
I : ModelWithCorners 𝕜 E H
M : Type u_4
inst✝⁶ : TopologicalSpace M
inst✝⁵ : ChartedSpace H M
E' : Type u_5
inst✝⁴ : NormedAddCommGroup E'
inst✝³ : NormedSpace 𝕜 E'
H' : Type u_6
inst✝² : TopologicalSpace H'
N : Type u_7
inst✝¹ : TopologicalSpace N
inst✝ : ChartedSpace H' N
J : ModelWithCorners 𝕜 E' H'
p : M × N
aux : interior (range ↑I) ×ˢ interior (range ↑J) = interior (range ↑(I.prod J))
hp : p ∈ ModelWithCorners.interior M ×ˢ ModelWithCorners.interior N
⊢ (↑(extChartAt (I.prod J) p) p).1 ∈ interior (range ↑I) ∧ (↑(extChartAt (I.prod J) p) p).2 ∈ interior (range ↑J)

Tactic:
obtain h := Set.mem_prod.mp hp

Result:
case h.mpr
𝕜 : Type u_1
inst✝¹⁰ : NontriviallyNormedField 𝕜
E : Type u_2
inst✝⁹ : NormedAddCommGroup E
inst✝⁸ : NormedSpace 𝕜 E
H : Type u_3
inst✝⁷ : TopologicalSpace H
I : ModelWithCorners 𝕜 E H
M : Type u_4
inst✝⁶ : TopologicalSpace M
inst✝⁵ : ChartedSpace H M
E' : Type u_5
inst✝⁴ : NormedAddCommGroup E'
inst✝³ : NormedSpace 𝕜 E'
H' : Type u_6
inst✝² : TopologicalSpace H'
N : Type u_7
inst✝¹ : TopologicalSpace N
inst✝ : ChartedSpace H' N
J : ModelWithCorners 𝕜 E' H'
p : M × N
aux : interior (range ↑I) ×ˢ interior (range ↑J) = interior (range ↑(I.prod J))
hp : p ∈ ModelWithCorners.interior M ×ˢ ModelWithCorners.interior N
h : p.1 ∈ ModelWithCorners.interior M ∧ p.2 ∈ ModelWithCorners.interior N
⊢ (↑(extChartAt (I.prod J) p) p).1 ∈ interior (range ↑I) ∧ (↑(extChartAt (I.prod J) p) p).2 ∈ interior (range ↑J)

Proof state:
case h.mpr
𝕜 : Type u_1
inst✝¹⁰ : NontriviallyNormedField 𝕜
E : Type u_2
inst✝⁹ : NormedAddCommGroup E
inst✝⁸ : NormedSpace 𝕜 E
H : Type u_3
inst✝⁷ : TopologicalSpace H
I : ModelWithCorners 𝕜 E H
M : Type u_4
inst✝⁶ : TopologicalSpace M
inst✝⁵ : ChartedSpace H M
E' : Type u_5
inst✝⁴ : NormedAddCommGroup E'
inst✝³ : NormedSpace 𝕜 E'
H' : Type u_6
inst✝² : TopologicalSpace H'
N : Type u_7
inst✝¹ : TopologicalSpace N
inst✝ : ChartedSpace H' N
J : ModelWithCorners 𝕜 E' H'
p : M × N
aux : interior (range ↑I) ×ˢ interior (range ↑J) = interior (range ↑(I.prod J))
hp : p ∈ ModelWithCorners.interior M ×ˢ ModelWithCorners.interior N
⊢ p ∈ ModelWithCorners.interior (M × N)

Tactic:
show (I.prod J).IsInteriorPoint p

Result:
case h.mpr
𝕜 : Type u_1
inst✝¹⁰ : NontriviallyNormedField 𝕜
E : Type u_2
inst✝⁹ : NormedAddCommGroup E
inst✝⁸ : NormedSpace 𝕜 E
H : Type u_3
inst✝⁷ : TopologicalSpace H
I : ModelWithCorners 𝕜 E H
M : Type u_4
inst✝⁶ : TopologicalSpace M
inst✝⁵ : ChartedSpace H M
E' : Type u_5
inst✝⁴ : NormedAddCommGroup E'
inst✝³ : NormedSpace 𝕜 E'
H' : Type u_6
inst✝² : TopologicalSpace H'
N : Type u_7
inst✝¹ : TopologicalSpace N
inst✝ : ChartedSpace H' N
J : ModelWithCorners 𝕜 E' H'
p : M × N
aux : interior (range ↑I) ×ˢ interior (range ↑J) = interior (range ↑(I.prod J))
hp : p ∈ ModelWithCorners.interior M ×ˢ ModelWithCorners.interior N
⊢ (I.prod J).IsInteriorPoint p