Theorem: Irrational.eventually_forall_le_dist_cast_div
File: Mathlib/Topology/Instances/Irrational.lean

tactic: have A : IsClosed (range (fun m => (n : ℝ)⁻¹ * m : ℤ → ℝ)) :=
  ((isClosedMap_smul₀ (n⁻¹ : ℝ)).comp Int.closedEmbedding_coe_real.isClosedMap).isClosed_range
state_before: x : ℝ
hx : Irrational x
n : ℕ
⊢ ∀ᶠ (ε : ℝ) in 𝓝 0, ∀ (m : ℤ), ε ≤ dist x (↑m / ↑n)
state_after: x : ℝ
hx : Irrational x
n : ℕ
A : IsClosed (range fun m => (↑n)⁻¹ * ↑m)
⊢ ∀ᶠ (ε : ℝ) in 𝓝 0, ∀ (m : ℤ), ε ≤ dist x (↑m / ↑n)

tactic: have B : x ∉ range (fun m => (n : ℝ)⁻¹ * m : ℤ → ℝ) := by
  rintro ⟨m, rfl⟩
  simp at hx
state_before: x : ℝ
hx : Irrational x
n : ℕ
A : IsClosed (range fun m => (↑n)⁻¹ * ↑m)
⊢ ∀ᶠ (ε : ℝ) in 𝓝 0, ∀ (m : ℤ), ε ≤ dist x (↑m / ↑n)
state_after: x : ℝ
hx : Irrational x
n : ℕ
A : IsClosed (range fun m => (↑n)⁻¹ * ↑m)
B : x ∉ range fun m => (↑n)⁻¹ * ↑m
⊢ ∀ᶠ (ε : ℝ) in 𝓝 0, ∀ (m : ℤ), ε ≤ dist x (↑m / ↑n)

tactic: rcases Metric.mem_nhds_iff.1 (A.isOpen_compl.mem_nhds B) with ⟨ε, ε0, hε⟩
state_before: x : ℝ
hx : Irrational x
n : ℕ
A : IsClosed (range fun m => (↑n)⁻¹ * ↑m)
B : x ∉ range fun m => (↑n)⁻¹ * ↑m
⊢ ∀ᶠ (ε : ℝ) in 𝓝 0, ∀ (m : ℤ), ε ≤ dist x (↑m / ↑n)
state_after: case intro.intro
x : ℝ
hx : Irrational x
n : ℕ
A : IsClosed (range fun m => (↑n)⁻¹ * ↑m)
B : x ∉ range fun m => (↑n)⁻¹ * ↑m
ε : ℝ
ε0 : ε > 0
hε : ball x ε ⊆ (range fun m => (↑n)⁻¹ * ↑m)ᶜ
⊢ ∀ᶠ (ε : ℝ) in 𝓝 0, ∀ (m : ℤ), ε ≤ dist x (↑m / ↑n)

tactic: refine (ge_mem_nhds ε0).mono fun δ hδ m => not_lt.1 fun hlt => ?_
state_before: case intro.intro
x : ℝ
hx : Irrational x
n : ℕ
A : IsClosed (range fun m => (↑n)⁻¹ * ↑m)
B : x ∉ range fun m => (↑n)⁻¹ * ↑m
ε : ℝ
ε0 : ε > 0
hε : ball x ε ⊆ (range fun m => (↑n)⁻¹ * ↑m)ᶜ
⊢ ∀ᶠ (ε : ℝ) in 𝓝 0, ∀ (m : ℤ), ε ≤ dist x (↑m / ↑n)
state_after: case intro.intro
x : ℝ
hx : Irrational x
n : ℕ
A : IsClosed (range fun m => (↑n)⁻¹ * ↑m)
B : x ∉ range fun m => (↑n)⁻¹ * ↑m
ε : ℝ
ε0 : ε > 0
hε : ball x ε ⊆ (range fun m => (↑n)⁻¹ * ↑m)ᶜ
δ : ℝ
hδ : δ ≤ ε
m : ℤ
hlt : dist x (↑m / ↑n) < δ
⊢ False

tactic: rw [dist_comm] at hlt
state_before: case intro.intro
x : ℝ
hx : Irrational x
n : ℕ
A : IsClosed (range fun m => (↑n)⁻¹ * ↑m)
B : x ∉ range fun m => (↑n)⁻¹ * ↑m
ε : ℝ
ε0 : ε > 0
hε : ball x ε ⊆ (range fun m => (↑n)⁻¹ * ↑m)ᶜ
δ : ℝ
hδ : δ ≤ ε
m : ℤ
hlt : dist x (↑m / ↑n) < δ
⊢ False
state_after: case intro.intro
x : ℝ
hx : Irrational x
n : ℕ
A : IsClosed (range fun m => (↑n)⁻¹ * ↑m)
B : x ∉ range fun m => (↑n)⁻¹ * ↑m
ε : ℝ
ε0 : ε > 0
hε : ball x ε ⊆ (range fun m => (↑n)⁻¹ * ↑m)ᶜ
δ : ℝ
hδ : δ ≤ ε
m : ℤ
hlt : dist (↑m / ↑n) x < δ
⊢ False

tactic: refine hε (ball_subset_ball hδ hlt) ⟨m, ?_⟩
state_before: case intro.intro
x : ℝ
hx : Irrational x
n : ℕ
A : IsClosed (range fun m => (↑n)⁻¹ * ↑m)
B : x ∉ range fun m => (↑n)⁻¹ * ↑m
ε : ℝ
ε0 : ε > 0
hε : ball x ε ⊆ (range fun m => (↑n)⁻¹ * ↑m)ᶜ
δ : ℝ
hδ : δ ≤ ε
m : ℤ
hlt : dist (↑m / ↑n) x < δ
⊢ False
state_after: case intro.intro
x : ℝ
hx : Irrational x
n : ℕ
A : IsClosed (range fun m => (↑n)⁻¹ * ↑m)
B : x ∉ range fun m => (↑n)⁻¹ * ↑m
ε : ℝ
ε0 : ε > 0
hε : ball x ε ⊆ (range fun m => (↑n)⁻¹ * ↑m)ᶜ
δ : ℝ
hδ : δ ≤ ε
m : ℤ
hlt : dist (↑m / ↑n) x < δ
⊢ (fun m => (↑n)⁻¹ * ↑m) m = ↑m / ↑n

tactic: simp [div_eq_inv_mul]
state_before: case intro.intro
x : ℝ
hx : Irrational x
n : ℕ
A : IsClosed (range fun m => (↑n)⁻¹ * ↑m)
B : x ∉ range fun m => (↑n)⁻¹ * ↑m
ε : ℝ
ε0 : ε > 0
hε : ball x ε ⊆ (range fun m => (↑n)⁻¹ * ↑m)ᶜ
δ : ℝ
hδ : δ ≤ ε
m : ℤ
hlt : dist (↑m / ↑n) x < δ
⊢ (fun m => (↑n)⁻¹ * ↑m) m = ↑m / ↑n
state_after: no goals

tactic: rintro ⟨m, rfl⟩
state_before: x : ℝ
hx : Irrational x
n : ℕ
A : IsClosed (range fun m => (↑n)⁻¹ * ↑m)
⊢ x ∉ range fun m => (↑n)⁻¹ * ↑m
state_after: case intro
n : ℕ
A : IsClosed (range fun m => (↑n)⁻¹ * ↑m)
m : ℤ
hx : Irrational ((fun m => (↑n)⁻¹ * ↑m) m)
⊢ False

tactic: simp at hx
state_before: case intro
n : ℕ
A : IsClosed (range fun m => (↑n)⁻¹ * ↑m)
m : ℤ
hx : Irrational ((fun m => (↑n)⁻¹ * ↑m) m)
⊢ False
state_after: no goals