-- Mathlib/Algebra/Order/CauSeq/Basic.lean
theorem rat_inv_continuous_lemma {β : Type*} [DivisionRing β] (abv : β → α) [IsAbsoluteValue abv]
    {ε K : α} (ε0 : 0 < ε) (K0 : 0 < K) :
    ∃ δ > 0, ∀ {a b : β}, K ≤ abv a → K ≤ abv b → abv (a - b) < δ → abv (a⁻¹ - b⁻¹) < ε

Proof state:
α : Type u_1
inst✝² : LinearOrderedField α
β : Type u_3
inst✝¹ : DivisionRing β
abv : β → α
inst✝ : IsAbsoluteValue abv
ε K : α
ε0 : 0 < ε
K0 : 0 < K
a b : β
ha : K ≤ abv a
hb : K ≤ abv b
h : abv (a - b) < K * ε * K
a0 : 0 < abv a
b0 : 0 < abv b
⊢ K * ε * K ≤ abv a * ε * abv b

Tactic:
gcongr

Result:
no goals

Proof state:
α : Type u_1
inst✝² : LinearOrderedField α
β : Type u_3
inst✝¹ : DivisionRing β
abv : β → α
inst✝ : IsAbsoluteValue abv
ε K : α
ε0 : 0 < ε
K0 : 0 < K
a b : β
ha : K ≤ abv a
hb : K ≤ abv b
h : abv (a - b) < K * ε * K
a0 : 0 < abv a
b0 : 0 < abv b
⊢ (abv a)⁻¹ * abv (a - b) * (abv b)⁻¹ < ε

Tactic:
refine lt_of_mul_lt_mul_left (lt_of_mul_lt_mul_right ?_ b0.le) a0.le

Result:
α : Type u_1
inst✝² : LinearOrderedField α
β : Type u_3
inst✝¹ : DivisionRing β
abv : β → α
inst✝ : IsAbsoluteValue abv
ε K : α
ε0 : 0 < ε
K0 : 0 < K
a b : β
ha : K ≤ abv a
hb : K ≤ abv b
h : abv (a - b) < K * ε * K
a0 : 0 < abv a
b0 : 0 < abv b
⊢ abv a * ((abv a)⁻¹ * abv (a - b) * (abv b)⁻¹) * abv b < abv a * ε * abv b

Proof state:
α : Type u_1
inst✝² : LinearOrderedField α
β : Type u_3
inst✝¹ : DivisionRing β
abv : β → α
inst✝ : IsAbsoluteValue abv
ε K : α
ε0 : 0 < ε
K0 : 0 < K
a b : β
ha : K ≤ abv a
hb : K ≤ abv b
h : abv (a - b) < K * ε * K
⊢ abv (a⁻¹ - b⁻¹) < ε

Tactic:
have a0 := K0.trans_le ha

Result:
α : Type u_1
inst✝² : LinearOrderedField α
β : Type u_3
inst✝¹ : DivisionRing β
abv : β → α
inst✝ : IsAbsoluteValue abv
ε K : α
ε0 : 0 < ε
K0 : 0 < K
a b : β
ha : K ≤ abv a
hb : K ≤ abv b
h : abv (a - b) < K * ε * K
a0 : 0 < abv a
⊢ abv (a⁻¹ - b⁻¹) < ε

Proof state:
α : Type u_1
inst✝² : LinearOrderedField α
β : Type u_3
inst✝¹ : DivisionRing β
abv : β → α
inst✝ : IsAbsoluteValue abv
ε K : α
ε0 : 0 < ε
K0 : 0 < K
a b : β
ha : K ≤ abv a
hb : K ≤ abv b
h : abv (a - b) < K * ε * K
a0 : 0 < abv a
b0 : 0 < abv b
⊢ abv a * ((abv a)⁻¹ * abv (a - b) * (abv b)⁻¹) * abv b < abv a * ε * abv b

Tactic:
rw [mul_assoc, inv_mul_cancel_right₀ b0.ne', ← mul_assoc, mul_inv_cancel₀ a0.ne', one_mul]

Result:
α : Type u_1
inst✝² : LinearOrderedField α
β : Type u_3
inst✝¹ : DivisionRing β
abv : β → α
inst✝ : IsAbsoluteValue abv
ε K : α
ε0 : 0 < ε
K0 : 0 < K
a b : β
ha : K ≤ abv a
hb : K ≤ abv b
h : abv (a - b) < K * ε * K
a0 : 0 < abv a
b0 : 0 < abv b
⊢ abv (a - b) < abv a * ε * abv b

Proof state:
α : Type u_1
inst✝² : LinearOrderedField α
β : Type u_3
inst✝¹ : DivisionRing β
abv : β → α
inst✝ : IsAbsoluteValue abv
ε K : α
ε0 : 0 < ε
K0 : 0 < K
a b : β
ha : K ≤ abv a
hb : K ≤ abv b
h : abv (a - b) < K * ε * K
a0 : 0 < abv a
b0 : 0 < abv b
⊢ abv (a - b) < abv a * ε * abv b

Tactic:
refine h.trans_le ?_

Result:
α : Type u_1
inst✝² : LinearOrderedField α
β : Type u_3
inst✝¹ : DivisionRing β
abv : β → α
inst✝ : IsAbsoluteValue abv
ε K : α
ε0 : 0 < ε
K0 : 0 < K
a b : β
ha : K ≤ abv a
hb : K ≤ abv b
h : abv (a - b) < K * ε * K
a0 : 0 < abv a
b0 : 0 < abv b
⊢ K * ε * K ≤ abv a * ε * abv b

Proof state:
α : Type u_1
inst✝² : LinearOrderedField α
β : Type u_3
inst✝¹ : DivisionRing β
abv : β → α
inst✝ : IsAbsoluteValue abv
ε K : α
ε0 : 0 < ε
K0 : 0 < K
a b : β
ha : K ≤ abv a
hb : K ≤ abv b
h : abv (a - b) < K * ε * K
a0 : 0 < abv a
b0 : 0 < abv b
⊢ abv (a⁻¹ - b⁻¹) < ε

Tactic:
rw [inv_sub_inv' ((abv_pos abv).1 a0) ((abv_pos abv).1 b0), abv_mul abv, abv_mul abv, abv_inv abv,
  abv_inv abv, abv_sub abv]

Result:
α : Type u_1
inst✝² : LinearOrderedField α
β : Type u_3
inst✝¹ : DivisionRing β
abv : β → α
inst✝ : IsAbsoluteValue abv
ε K : α
ε0 : 0 < ε
K0 : 0 < K
a b : β
ha : K ≤ abv a
hb : K ≤ abv b
h : abv (a - b) < K * ε * K
a0 : 0 < abv a
b0 : 0 < abv b
⊢ (abv a)⁻¹ * abv (a - b) * (abv b)⁻¹ < ε

Proof state:
α : Type u_1
inst✝² : LinearOrderedField α
β : Type u_3
inst✝¹ : DivisionRing β
abv : β → α
inst✝ : IsAbsoluteValue abv
ε K : α
ε0 : 0 < ε
K0 : 0 < K
⊢ ∃ δ > 0, ∀ {a b : β}, K ≤ abv a → K ≤ abv b → abv (a - b) < δ → abv (a⁻¹ - b⁻¹) < ε

Tactic:
refine ⟨K * ε * K, mul_pos (mul_pos K0 ε0) K0, fun {a b} ha hb h => ?_⟩

Result:
α : Type u_1
inst✝² : LinearOrderedField α
β : Type u_3
inst✝¹ : DivisionRing β
abv : β → α
inst✝ : IsAbsoluteValue abv
ε K : α
ε0 : 0 < ε
K0 : 0 < K
a b : β
ha : K ≤ abv a
hb : K ≤ abv b
h : abv (a - b) < K * ε * K
⊢ abv (a⁻¹ - b⁻¹) < ε

Proof state:
α : Type u_1
inst✝² : LinearOrderedField α
β : Type u_3
inst✝¹ : DivisionRing β
abv : β → α
inst✝ : IsAbsoluteValue abv
ε K : α
ε0 : 0 < ε
K0 : 0 < K
a b : β
ha : K ≤ abv a
hb : K ≤ abv b
h : abv (a - b) < K * ε * K
a0 : 0 < abv a
⊢ abv (a⁻¹ - b⁻¹) < ε

Tactic:
have b0 := K0.trans_le hb

Result:
α : Type u_1
inst✝² : LinearOrderedField α
β : Type u_3
inst✝¹ : DivisionRing β
abv : β → α
inst✝ : IsAbsoluteValue abv
ε K : α
ε0 : 0 < ε
K0 : 0 < K
a b : β
ha : K ≤ abv a
hb : K ≤ abv b
h : abv (a - b) < K * ε * K
a0 : 0 < abv a
b0 : 0 < abv b
⊢ abv (a⁻¹ - b⁻¹) < ε