Theorem: CauSeq.of_near
File: Mathlib/Algebra/Order/CauSeq/Basic.lean

Proof steps:
state_before: α : Type u_1
β : Type u_2
inst✝² : LinearOrderedField α
inst✝¹ : Ring β
abv : β → α
inst✝ : IsAbsoluteValue abv
f : ℕ → β
g : CauSeq β abv
h : ∀ ε > 0, ∃ i, ∀ j ≥ i, abv (f j - ↑g j) < ε
ε : α
ε0 : ε > 0
i : ℕ
hi : ∀ j ≥ i, abv (f j - ↑g j) < ε / 2 / 2 ∧ ∀ k ≥ j, abv (↑g k - ↑g j) < ε / 2
j : ℕ
ij : j ≥ i
⊢ abv (f j - f i) < ε
state_after: case intro
α : Type u_1
β : Type u_2
inst✝² : LinearOrderedField α
inst✝¹ : Ring β
abv : β → α
inst✝ : IsAbsoluteValue abv
f : ℕ → β
g : CauSeq β abv
h : ∀ ε > 0, ∃ i, ∀ j ≥ i, abv (f j - ↑g j) < ε
ε : α
ε0 : ε > 0
i : ℕ
hi : ∀ j ≥ i, abv (f j - ↑g j) < ε / 2 / 2 ∧ ∀ k ≥ j, abv (↑g k - ↑g j) < ε / 2
j : ℕ
ij : j ≥ i
h₁ : abv (f i - ↑g i) < ε / 2 / 2
h₂ : ∀ k ≥ i, abv (↑g k - ↑g i) < ε / 2
⊢ abv (f j - f i) < ε
tactic: cases' hi _ le_rfl with h₁ h₂
state_before: case intro
α : Type u_1
β : Type u_2
inst✝² : LinearOrderedField α
inst✝¹ : Ring β
abv : β → α
inst✝ : IsAbsoluteValue abv
f : ℕ → β
g : CauSeq β abv
h : ∀ ε > 0, ∃ i, ∀ j ≥ i, abv (f j - ↑g j) < ε
ε : α
ε0 : ε > 0
i : ℕ
hi : ∀ j ≥ i, abv (f j - ↑g j) < ε / 2 / 2 ∧ ∀ k ≥ j, abv (↑g k - ↑g j) < ε / 2
j : ℕ
ij : j ≥ i
h₁ : abv (f i - ↑g i) < ε / 2 / 2
h₂ : ∀ k ≥ i, abv (↑g k - ↑g i) < ε / 2
⊢ abv (f j - f i) < ε
state_after: case intro
α : Type u_1
β : Type u_2
inst✝² : LinearOrderedField α
inst✝¹ : Ring β
abv : β → α
inst✝ : IsAbsoluteValue abv
f : ℕ → β
g : CauSeq β abv
h : ∀ ε > 0, ∃ i, ∀ j ≥ i, abv (f j - ↑g j) < ε
ε : α
ε0 : ε > 0
i : ℕ
hi : ∀ j ≥ i, abv (f j - ↑g j) < ε / 2 / 2 ∧ ∀ k ≥ j, abv (↑g k - ↑g j) < ε / 2
j : ℕ
ij : j ≥ i
h₁ : abv (↑g i - f i) < ε / 2 / 2
h₂ : ∀ k ≥ i, abv (↑g k - ↑g i) < ε / 2
⊢ abv (f j - f i) < ε
tactic: rw [abv_sub abv] at h₁
state_before: case intro
α : Type u_1
β : Type u_2
inst✝² : LinearOrderedField α
inst✝¹ : Ring β
abv : β → α
inst✝ : IsAbsoluteValue abv
f : ℕ → β
g : CauSeq β abv
h : ∀ ε > 0, ∃ i, ∀ j ≥ i, abv (f j - ↑g j) < ε
ε : α
ε0 : ε > 0
i : ℕ
hi : ∀ j ≥ i, abv (f j - ↑g j) < ε / 2 / 2 ∧ ∀ k ≥ j, abv (↑g k - ↑g j) < ε / 2
j : ℕ
ij : j ≥ i
h₁ : abv (↑g i - f i) < ε / 2 / 2
h₂ : ∀ k ≥ i, abv (↑g k - ↑g i) < ε / 2
⊢ abv (f j - f i) < ε
state_after: case intro
α : Type u_1
β : Type u_2
inst✝² : LinearOrderedField α
inst✝¹ : Ring β
abv : β → α
inst✝ : IsAbsoluteValue abv
f : ℕ → β
g : CauSeq β abv
h : ∀ ε > 0, ∃ i, ∀ j ≥ i, abv (f j - ↑g j) < ε
ε : α
ε0 : ε > 0
i : ℕ
hi : ∀ j ≥ i, abv (f j - ↑g j) < ε / 2 / 2 ∧ ∀ k ≥ j, abv (↑g k - ↑g j) < ε / 2
j : ℕ
ij : j ≥ i
h₁ : abv (↑g i - f i) < ε / 2 / 2
h₂ : ∀ k ≥ i, abv (↑g k - ↑g i) < ε / 2
this : abv (f j - ↑g j + (↑g i - f i)) < ε / 2 / 2 + ε / 2 / 2
⊢ abv (f j - f i) < ε
tactic: have := lt_of_le_of_lt (abv_add abv _ _) (add_lt_add (hi _ ij).1 h₁)
state_before: case intro
α : Type u_1
β : Type u_2
inst✝² : LinearOrderedField α
inst✝¹ : Ring β
abv : β → α
inst✝ : IsAbsoluteValue abv
f : ℕ → β
g : CauSeq β abv
h : ∀ ε > 0, ∃ i, ∀ j ≥ i, abv (f j - ↑g j) < ε
ε : α
ε0 : ε > 0
i : ℕ
hi : ∀ j ≥ i, abv (f j - ↑g j) < ε / 2 / 2 ∧ ∀ k ≥ j, abv (↑g k - ↑g j) < ε / 2
j : ℕ
ij : j ≥ i
h₁ : abv (↑g i - f i) < ε / 2 / 2
h₂ : ∀ k ≥ i, abv (↑g k - ↑g i) < ε / 2
this : abv (f j - ↑g j + (↑g i - f i)) < ε / 2 / 2 + ε / 2 / 2
⊢ abv (f j - f i) < ε
state_after: case intro
α : Type u_1
β : Type u_2
inst✝² : LinearOrderedField α
inst✝¹ : Ring β
abv : β → α
inst✝ : IsAbsoluteValue abv
f : ℕ → β
g : CauSeq β abv
h : ∀ ε > 0, ∃ i, ∀ j ≥ i, abv (f j - ↑g j) < ε
ε : α
ε0 : ε > 0
i : ℕ
hi : ∀ j ≥ i, abv (f j - ↑g j) < ε / 2 / 2 ∧ ∀ k ≥ j, abv (↑g k - ↑g j) < ε / 2
j : ℕ
ij : j ≥ i
h₁ : abv (↑g i - f i) < ε / 2 / 2
h₂ : ∀ k ≥ i, abv (↑g k - ↑g i) < ε / 2
this✝ : abv (f j - ↑g j + (↑g i - f i)) < ε / 2 / 2 + ε / 2 / 2
this : abv (f j - ↑g j + (↑g i - f i) + (↑g j - ↑g i)) < ε / 2 / 2 + ε / 2 / 2 + ε / 2
⊢ abv (f j - f i) < ε
tactic: have := lt_of_le_of_lt (abv_add abv _ _) (add_lt_add this (h₂ _ ij))
state_before: case intro
α : Type u_1
β : Type u_2
inst✝² : LinearOrderedField α
inst✝¹ : Ring β
abv : β → α
inst✝ : IsAbsoluteValue abv
f : ℕ → β
g : CauSeq β abv
h : ∀ ε > 0, ∃ i, ∀ j ≥ i, abv (f j - ↑g j) < ε
ε : α
ε0 : ε > 0
i : ℕ
hi : ∀ j ≥ i, abv (f j - ↑g j) < ε / 2 / 2 ∧ ∀ k ≥ j, abv (↑g k - ↑g j) < ε / 2
j : ℕ
ij : j ≥ i
h₁ : abv (↑g i - f i) < ε / 2 / 2
h₂ : ∀ k ≥ i, abv (↑g k - ↑g i) < ε / 2
this✝ : abv (f j - ↑g j + (↑g i - f i)) < ε / 2 / 2 + ε / 2 / 2
this : abv (f j - ↑g j + (↑g i - f i) + (↑g j - ↑g i)) < ε / 2 / 2 + ε / 2 / 2 + ε / 2
⊢ abv (f j - f i) < ε
state_after: no goals
tactic: rwa [add_halves, add_halves, add_right_comm, sub_add_sub_cancel, sub_add_sub_cancel] at this