-- Mathlib/Analysis/LocallyConvex/Basic.lean
theorem Balanced.zero_insert_interior (hA : Balanced 𝕜 A) :
    Balanced 𝕜 (insert 0 (interior A))

Proof state:
case inl
𝕜 : Type u_1
E : Type u_3
inst✝⁴ : NormedField 𝕜
inst✝³ : AddCommGroup E
inst✝² : Module 𝕜 E
A : Set E
inst✝¹ : TopologicalSpace E
inst✝ : ContinuousSMul 𝕜 E
hA : Balanced 𝕜 A
ha : ‖0‖ ≤ 1
⊢ 0 ⊆ insert 0 (interior A)

case inl
𝕜 : Type u_1
E : Type u_3
inst✝⁴ : NormedField 𝕜
inst✝³ : AddCommGroup E
inst✝² : Module 𝕜 E
A : Set E
inst✝¹ : TopologicalSpace E
inst✝ : ContinuousSMul 𝕜 E
hA : Balanced 𝕜 A
ha : ‖0‖ ≤ 1
⊢ (insert 0 (interior A)).Nonempty

Tactic:
exacts [subset_union_left, ⟨0, Or.inl rfl⟩]

Result:
no goals

Proof state:
case inr
𝕜 : Type u_1
E : Type u_3
inst✝⁴ : NormedField 𝕜
inst✝³ : AddCommGroup E
inst✝² : Module 𝕜 E
A : Set E
inst✝¹ : TopologicalSpace E
inst✝ : ContinuousSMul 𝕜 E
hA : Balanced 𝕜 A
a : 𝕜
ha : ‖a‖ ≤ 1
h : a ≠ 0
⊢ insert 0 ((fun x => a • x) '' interior A) ⊆ insert 0 (interior A)

Tactic:
apply insert_subset_insert

Result:
case inr.h
𝕜 : Type u_1
E : Type u_3
inst✝⁴ : NormedField 𝕜
inst✝³ : AddCommGroup E
inst✝² : Module 𝕜 E
A : Set E
inst✝¹ : TopologicalSpace E
inst✝ : ContinuousSMul 𝕜 E
hA : Balanced 𝕜 A
a : 𝕜
ha : ‖a‖ ≤ 1
h : a ≠ 0
⊢ (fun x => a • x) '' interior A ⊆ interior A

Proof state:
case inr
𝕜 : Type u_1
E : Type u_3
inst✝⁴ : NormedField 𝕜
inst✝³ : AddCommGroup E
inst✝² : Module 𝕜 E
A : Set E
inst✝¹ : TopologicalSpace E
inst✝ : ContinuousSMul 𝕜 E
hA : Balanced 𝕜 A
a : 𝕜
ha : ‖a‖ ≤ 1
h : a ≠ 0
⊢ a • insert 0 (interior A) ⊆ insert 0 (interior A)

Tactic:
rw [← image_smul, image_insert_eq, smul_zero]

Result:
case inr
𝕜 : Type u_1
E : Type u_3
inst✝⁴ : NormedField 𝕜
inst✝³ : AddCommGroup E
inst✝² : Module 𝕜 E
A : Set E
inst✝¹ : TopologicalSpace E
inst✝ : ContinuousSMul 𝕜 E
hA : Balanced 𝕜 A
a : 𝕜
ha : ‖a‖ ≤ 1
h : a ≠ 0
⊢ insert 0 ((fun x => a • x) '' interior A) ⊆ insert 0 (interior A)

Proof state:
case inr.h
𝕜 : Type u_1
E : Type u_3
inst✝⁴ : NormedField 𝕜
inst✝³ : AddCommGroup E
inst✝² : Module 𝕜 E
A : Set E
inst✝¹ : TopologicalSpace E
inst✝ : ContinuousSMul 𝕜 E
hA : Balanced 𝕜 A
a : 𝕜
ha : ‖a‖ ≤ 1
h : a ≠ 0
⊢ (fun x => a • x) '' interior A ⊆ interior A

Tactic:
exact ((isOpenMap_smul₀ h).mapsTo_interior <| hA.smul_mem ha).image_subset

Result:
no goals

Proof state:
𝕜 : Type u_1
E : Type u_3
inst✝⁴ : NormedField 𝕜
inst✝³ : AddCommGroup E
inst✝² : Module 𝕜 E
A : Set E
inst✝¹ : TopologicalSpace E
inst✝ : ContinuousSMul 𝕜 E
hA : Balanced 𝕜 A
a : 𝕜
ha : ‖a‖ ≤ 1
⊢ a • insert 0 (interior A) ⊆ insert 0 (interior A)

Tactic:
obtain rfl | h := eq_or_ne a 0

Result:
case inl
𝕜 : Type u_1
E : Type u_3
inst✝⁴ : NormedField 𝕜
inst✝³ : AddCommGroup E
inst✝² : Module 𝕜 E
A : Set E
inst✝¹ : TopologicalSpace E
inst✝ : ContinuousSMul 𝕜 E
hA : Balanced 𝕜 A
ha : ‖0‖ ≤ 1
⊢ 0 • insert 0 (interior A) ⊆ insert 0 (interior A)

case inr
𝕜 : Type u_1
E : Type u_3
inst✝⁴ : NormedField 𝕜
inst✝³ : AddCommGroup E
inst✝² : Module 𝕜 E
A : Set E
inst✝¹ : TopologicalSpace E
inst✝ : ContinuousSMul 𝕜 E
hA : Balanced 𝕜 A
a : 𝕜
ha : ‖a‖ ≤ 1
h : a ≠ 0
⊢ a • insert 0 (interior A) ⊆ insert 0 (interior A)

Proof state:
𝕜 : Type u_1
E : Type u_3
inst✝⁴ : NormedField 𝕜
inst✝³ : AddCommGroup E
inst✝² : Module 𝕜 E
A : Set E
inst✝¹ : TopologicalSpace E
inst✝ : ContinuousSMul 𝕜 E
hA : Balanced 𝕜 A
⊢ Balanced 𝕜 (insert 0 (interior A))

Tactic:
intro a ha

Result:
𝕜 : Type u_1
E : Type u_3
inst✝⁴ : NormedField 𝕜
inst✝³ : AddCommGroup E
inst✝² : Module 𝕜 E
A : Set E
inst✝¹ : TopologicalSpace E
inst✝ : ContinuousSMul 𝕜 E
hA : Balanced 𝕜 A
a : 𝕜
ha : ‖a‖ ≤ 1
⊢ a • insert 0 (interior A) ⊆ insert 0 (interior A)

Proof state:
case inl
𝕜 : Type u_1
E : Type u_3
inst✝⁴ : NormedField 𝕜
inst✝³ : AddCommGroup E
inst✝² : Module 𝕜 E
A : Set E
inst✝¹ : TopologicalSpace E
inst✝ : ContinuousSMul 𝕜 E
hA : Balanced 𝕜 A
ha : ‖0‖ ≤ 1
⊢ 0 • insert 0 (interior A) ⊆ insert 0 (interior A)

Tactic:
rw [zero_smul_set]

Result:
case inl
𝕜 : Type u_1
E : Type u_3
inst✝⁴ : NormedField 𝕜
inst✝³ : AddCommGroup E
inst✝² : Module 𝕜 E
A : Set E
inst✝¹ : TopologicalSpace E
inst✝ : ContinuousSMul 𝕜 E
hA : Balanced 𝕜 A
ha : ‖0‖ ≤ 1
⊢ 0 ⊆ insert 0 (interior A)

case inl
𝕜 : Type u_1
E : Type u_3
inst✝⁴ : NormedField 𝕜
inst✝³ : AddCommGroup E
inst✝² : Module 𝕜 E
A : Set E
inst✝¹ : TopologicalSpace E
inst✝ : ContinuousSMul 𝕜 E
hA : Balanced 𝕜 A
ha : ‖0‖ ≤ 1
⊢ (insert 0 (interior A)).Nonempty