l3lab/ntp-mathlib huggingface dataset:
/-- Adding a multiple of the second vector passed to `oangle` to the first vector does not change
the sign of the angle. -/
@[simp]
theorem oangle_sign_add_smul_left (x y : V) (r : ℝ) :
    (o.oangle (x + r • y) y).sign = (o.oangle x y).sign := by
  

Proof state:
V : Type u_1
V' : Type u_2
inst✝⁵ : NormedAddCommGroup V
inst✝⁴ : NormedAddCommGroup V'
inst✝³ : InnerProductSpace ℝ V
inst✝² : InnerProductSpace ℝ V'
inst✝¹ : Fact (finrank ℝ V = 2)
inst✝ : Fact (finrank ℝ V' = 2)
o : Orientation ℝ V (Fin 2)
x y : V
r : ℝ
⊢ Real.Angle.sign (oangle o (x + r • y) y) = Real.Angle.sign (oangle o x y)

Next tactic:
simp_rw [o.oangle_rev y, Real.Angle.sign_neg, add_comm x, oangle_sign_smul_add_right]
/-- Subtracting a multiple of the first vector passed to `oangle` from the second vector does
not change the sign of the angle. -/
@[simp]
theorem oangle_sign_sub_smul_right (x y : V) (r : ℝ) :
    (o.oangle x (y - r • x)).sign = (o.oangle x y).sign := by
  

Proof state:
V : Type u_1
V' : Type u_2
inst✝⁵ : NormedAddCommGroup V
inst✝⁴ : NormedAddCommGroup V'
inst✝³ : InnerProductSpace ℝ V
inst✝² : InnerProductSpace ℝ V'
inst✝¹ : Fact (finrank ℝ V = 2)
inst✝ : Fact (finrank ℝ V' = 2)
o : Orientation ℝ V (Fin 2)
x y : V
r : ℝ
⊢ Real.Angle.sign (oangle o x (y - r • x)) = Real.Angle.sign (oangle o x y)

Next tactic:
rw [sub_eq_add_neg, ← neg_smul, add_comm, oangle_sign_smul_add_right]
/-- Subtracting a multiple of the second vector passed to `oangle` from the first vector does
not change the sign of the angle. -/
@[simp]
theorem oangle_sign_sub_smul_left (x y : V) (r : ℝ) :
    (o.oangle (x - r • y) y).sign = (o.oangle x y).sign := by
  

Proof state:
V : Type u_1
V' : Type u_2
inst✝⁵ : NormedAddCommGroup V
inst✝⁴ : NormedAddCommGroup V'
inst✝³ : InnerProductSpace ℝ V
inst✝² : InnerProductSpace ℝ V'
inst✝¹ : Fact (finrank ℝ V = 2)
inst✝ : Fact (finrank ℝ V' = 2)
o : Orientation ℝ V (Fin 2)
x y : V
r : ℝ
⊢ Real.Angle.sign (oangle o (x - r • y) y) = Real.Angle.sign (oangle o x y)

Next tactic:
rw [sub_eq_add_neg, ← neg_smul, oangle_sign_add_smul_left]
/-- Adding the first vector passed to `oangle` to the second vector does not change the sign of
the angle. -/
@[simp]
theorem oangle_sign_add_right (x y : V) : (o.oangle x (x + y)).sign = (o.oangle x y).sign := by
  

Proof state:
V : Type u_1
V' : Type u_2
inst✝⁵ : NormedAddCommGroup V
inst✝⁴ : NormedAddCommGroup V'
inst✝³ : InnerProductSpace ℝ V
inst✝² : InnerProductSpace ℝ V'
inst✝¹ : Fact (finrank ℝ V = 2)
inst✝ : Fact (finrank ℝ V' = 2)
o : Orientation ℝ V (Fin 2)
x y : V
⊢ Real.Angle.sign (oangle o x (x + y)) = Real.Angle.sign (oangle o x y)

Next tactic:
rw [← o.oangle_sign_smul_add_right x y 1, one_smul]
/-- Adding the second vector passed to `oangle` to the first vector does not change the sign of
the angle. -/
@[simp]
theorem oangle_sign_add_left (x y : V) : (o.oangle (x + y) y).sign = (o.oangle x y).sign := by
  

Proof state:
V : Type u_1
V' : Type u_2
inst✝⁵ : NormedAddCommGroup V
inst✝⁴ : NormedAddCommGroup V'
inst✝³ : InnerProductSpace ℝ V
inst✝² : InnerProductSpace ℝ V'
inst✝¹ : Fact (finrank ℝ V = 2)
inst✝ : Fact (finrank ℝ V' = 2)
o : Orientation ℝ V (Fin 2)
x y : V
⊢ Real.Angle.sign (oangle o (x + y) y) = Real.Angle.sign (oangle o x y)

Next tactic:
rw [← o.oangle_sign_add_smul_left x y 1, one_smul]
/-- Subtracting the first vector passed to `oangle` from the second vector does not change the
sign of the angle. -/
@[simp]
theorem oangle_sign_sub_right (x y : V) : (o.oangle x (y - x)).sign = (o.oangle x y).sign := by
  

Proof state:
V : Type u_1
V' : Type u_2
inst✝⁵ : NormedAddCommGroup V
inst✝⁴ : NormedAddCommGroup V'
inst✝³ : InnerProductSpace ℝ V
inst✝² : InnerProductSpace ℝ V'
inst✝¹ : Fact (finrank ℝ V = 2)
inst✝ : Fact (finrank ℝ V' = 2)
o : Orientation ℝ V (Fin 2)
x y : V
⊢ Real.Angle.sign (oangle o x (y - x)) = Real.Angle.sign (oangle o x y)

Next tactic:
rw [← o.oangle_sign_sub_smul_right x y 1, one_smul]
/-- Subtracting the second vector passed to `oangle` from the first vector does not change the
sign of the angle. -/
@[simp]
theorem oangle_sign_sub_left (x y : V) : (o.oangle (x - y) y).sign = (o.oangle x y).sign := by
  

Proof state:
V : Type u_1
V' : Type u_2
inst✝⁵ : NormedAddCommGroup V
inst✝⁴ : NormedAddCommGroup V'
inst✝³ : InnerProductSpace ℝ V
inst✝² : InnerProductSpace ℝ V'
inst✝¹ : Fact (finrank ℝ V = 2)
inst✝ : Fact (finrank ℝ V' = 2)
o : Orientation ℝ V (Fin 2)
x y : V
⊢ Real.Angle.sign (oangle o (x - y) y) = Real.Angle.sign (oangle o x y)

Next tactic:
rw [← o.oangle_sign_sub_smul_left x y 1, one_smul]
/-- Subtracting the second vector passed to `oangle` from a multiple of the first vector negates
the sign of the angle. -/
@[simp]
theorem oangle_sign_smul_sub_right (x y : V) (r : ℝ) :
    (o.oangle x (r • x - y)).sign = -(o.oangle x y).sign := by
  

Proof state:
V : Type u_1
V' : Type u_2
inst✝⁵ : NormedAddCommGroup V
inst✝⁴ : NormedAddCommGroup V'
inst✝³ : InnerProductSpace ℝ V
inst✝² : InnerProductSpace ℝ V'
inst✝¹ : Fact (finrank ℝ V = 2)
inst✝ : Fact (finrank ℝ V' = 2)
o : Orientation ℝ V (Fin 2)
x y : V
r : ℝ
⊢ Real.Angle.sign (oangle o x (r • x - y)) = -Real.Angle.sign (oangle o x y)

Next tactic:
rw [← oangle_sign_neg_right, sub_eq_add_neg, oangle_sign_smul_add_right]
/-- Subtracting the first vector passed to `oangle` from a multiple of the second vector negates
the sign of the angle. -/
@[simp]
theorem oangle_sign_smul_sub_left (x y : V) (r : ℝ) :
    (o.oangle (r • y - x) y).sign = -(o.oangle x y).sign := by
  

Proof state:
V : Type u_1
V' : Type u_2
inst✝⁵ : NormedAddCommGroup V
inst✝⁴ : NormedAddCommGroup V'
inst✝³ : InnerProductSpace ℝ V
inst✝² : InnerProductSpace ℝ V'
inst✝¹ : Fact (finrank ℝ V = 2)
inst✝ : Fact (finrank ℝ V' = 2)
o : Orientation ℝ V (Fin 2)
x y : V
r : ℝ
⊢ Real.Angle.sign (oangle o (r • y - x) y) = -Real.Angle.sign (oangle o x y)

Next tactic:
rw [← oangle_sign_neg_left, sub_eq_neg_add, oangle_sign_add_smul_left]
/-- Subtracting the second vector passed to `oangle` from the first vector negates the sign of
the angle. -/
theorem oangle_sign_sub_right_eq_neg (x y : V) :
    (o.oangle x (x - y)).sign = -(o.oangle x y).sign := by
  

Proof state:
V : Type u_1
V' : Type u_2
inst✝⁵ : NormedAddCommGroup V
inst✝⁴ : NormedAddCommGroup V'
inst✝³ : InnerProductSpace ℝ V
inst✝² : InnerProductSpace ℝ V'
inst✝¹ : Fact (finrank ℝ V = 2)
inst✝ : Fact (finrank ℝ V' = 2)
o : Orientation ℝ V (Fin 2)
x y : V
⊢ Real.Angle.sign (oangle o x (x - y)) = -Real.Angle.sign (oangle o x y)

Next tactic:
rw [← o.oangle_sign_smul_sub_right x y 1, one_smul]
/-- Subtracting the first vector passed to `oangle` from the second vector negates the sign of
the angle. -/
theorem oangle_sign_sub_left_eq_neg (x y : V) :
    (o.oangle (y - x) y).sign = -(o.oangle x y).sign := by
  

Proof state:
V : Type u_1
V' : Type u_2
inst✝⁵ : NormedAddCommGroup V
inst✝⁴ : NormedAddCommGroup V'
inst✝³ : InnerProductSpace ℝ V
inst✝² : InnerProductSpace ℝ V'
inst✝¹ : Fact (finrank ℝ V = 2)
inst✝ : Fact (finrank ℝ V' = 2)
o : Orientation ℝ V (Fin 2)
x y : V
⊢ Real.Angle.sign (oangle o (y - x) y) = -Real.Angle.sign (oangle o x y)

Next tactic:
rw [← o.oangle_sign_smul_sub_left x y 1, one_smul]
/-- Subtracting the first vector passed to `oangle` from the second vector then swapping the
vectors does not change the sign of the angle. -/
@[simp]
theorem oangle_sign_sub_right_swap (x y : V) : (o.oangle y (y - x)).sign = (o.oangle x y).sign := by
  

Proof state:
V : Type u_1
V' : Type u_2
inst✝⁵ : NormedAddCommGroup V
inst✝⁴ : NormedAddCommGroup V'
inst✝³ : InnerProductSpace ℝ V
inst✝² : InnerProductSpace ℝ V'
inst✝¹ : Fact (finrank ℝ V = 2)
inst✝ : Fact (finrank ℝ V' = 2)
o : Orientation ℝ V (Fin 2)
x y : V
⊢ Real.Angle.sign (oangle o y (y - x)) = Real.Angle.sign (oangle o x y)

Next tactic:
rw [oangle_sign_sub_right_eq_neg, o.oangle_rev y x, Real.Angle.sign_neg]
/-- Subtracting the second vector passed to `oangle` from the first vector then swapping the
vectors does not change the sign of the angle. -/
@[simp]
theorem oangle_sign_sub_left_swap (x y : V) : (o.oangle (x - y) x).sign = (o.oangle x y).sign := by
  

Proof state:
V : Type u_1
V' : Type u_2
inst✝⁵ : NormedAddCommGroup V
inst✝⁴ : NormedAddCommGroup V'
inst✝³ : InnerProductSpace ℝ V
inst✝² : InnerProductSpace ℝ V'
inst✝¹ : Fact (finrank ℝ V = 2)
inst✝ : Fact (finrank ℝ V' = 2)
o : Orientation ℝ V (Fin 2)
x y : V
⊢ Real.Angle.sign (oangle o (x - y) x) = Real.Angle.sign (oangle o x y)

Next tactic:
rw [oangle_sign_sub_left_eq_neg, o.oangle_rev y x, Real.Angle.sign_neg]
/-- The sign of the angle between a vector, and a linear combination of that vector with a second
vector, is the sign of the factor by which the second vector is multiplied in that combination
multiplied by the sign of the angle between the two vectors. -/
-- @[simp] -- Porting note: simp can prove this
theorem oangle_sign_smul_add_smul_right (x y : V) (r₁ r₂ : ℝ) :
    (o.oangle x (r₁ • x + r₂ • y)).sign = SignType.sign r₂ * (o.oangle x y).sign := by
  

Proof state:
V : Type u_1
V' : Type u_2
inst✝⁵ : NormedAddCommGroup V
inst✝⁴ : NormedAddCommGroup V'
inst✝³ : InnerProductSpace ℝ V
inst✝² : InnerProductSpace ℝ V'
inst✝¹ : Fact (finrank ℝ V = 2)
inst✝ : Fact (finrank ℝ V' = 2)
o : Orientation ℝ V (Fin 2)
x y : V
r₁ r₂ : ℝ
⊢ Real.Angle.sign (oangle o x (r₁ • x + r₂ • y)) = SignType.sign r₂ * Real.Angle.sign (oangle o x y)

Next tactic:
rw [← o.oangle_sign_smul_add_right x (r₁ • x + r₂ • y) (-r₁)]
/-- The sign of the angle between a vector, and a linear combination of that vector with a second
vector, is the sign of the factor by which the second vector is multiplied in that combination
multiplied by the sign of the angle between the two vectors. -/
-- @[simp] -- Porting note: simp can prove this
theorem oangle_sign_smul_add_smul_right (x y : V) (r₁ r₂ : ℝ) :
    (o.oangle x (r₁ • x + r₂ • y)).sign = SignType.sign r₂ * (o.oangle x y).sign := by
  rw [← o.oangle_sign_smul_add_right x (r₁ • x + r₂ • y) (-r₁)]
  

Proof state:
V : Type u_1
V' : Type u_2
inst✝⁵ : NormedAddCommGroup V
inst✝⁴ : NormedAddCommGroup V'
inst✝³ : InnerProductSpace ℝ V
inst✝² : InnerProductSpace ℝ V'
inst✝¹ : Fact (finrank ℝ V = 2)
inst✝ : Fact (finrank ℝ V' = 2)
o : Orientation ℝ V (Fin 2)
x y : V
r₁ r₂ : ℝ
⊢ Real.Angle.sign (oangle o x (-r₁ • x + (r₁ • x + r₂ • y))) = SignType.sign r₂ * Real.Angle.sign (oangle o x y)

Next tactic:
simp
/-- The sign of the angle between a linear combination of two vectors and the second vector is
the sign of the factor by which the first vector is multiplied in that combination multiplied by
the sign of the angle between the two vectors. -/
-- @[simp] -- Porting note: simp can prove this
theorem oangle_sign_smul_add_smul_left (x y : V) (r₁ r₂ : ℝ) :
    (o.oangle (r₁ • x + r₂ • y) y).sign = SignType.sign r₁ * (o.oangle x y).sign := by
  

Proof state:
V : Type u_1
V' : Type u_2
inst✝⁵ : NormedAddCommGroup V
inst✝⁴ : NormedAddCommGroup V'
inst✝³ : InnerProductSpace ℝ V
inst✝² : InnerProductSpace ℝ V'
inst✝¹ : Fact (finrank ℝ V = 2)
inst✝ : Fact (finrank ℝ V' = 2)
o : Orientation ℝ V (Fin 2)
x y : V
r₁ r₂ : ℝ
⊢ Real.Angle.sign (oangle o (r₁ • x + r₂ • y) y) = SignType.sign r₁ * Real.Angle.sign (oangle o x y)

Next tactic:
simp_rw [o.oangle_rev y, Real.Angle.sign_neg, add_comm (r₁ • x), oangle_sign_smul_add_smul_right,
    mul_neg]
/-- The sign of the angle between two linear combinations of two vectors is the sign of the
determinant of the factors in those combinations multiplied by the sign of the angle between the
two vectors. -/
theorem oangle_sign_smul_add_smul_smul_add_smul (x y : V) (r₁ r₂ r₃ r₄ : ℝ) :
    (o.oangle (r₁ • x + r₂ • y) (r₃ • x + r₄ • y)).sign =
      SignType.sign (r₁ * r₄ - r₂ * r₃) * (o.oangle x y).sign := by
  

Proof state:
V : Type u_1
V' : Type u_2
inst✝⁵ : NormedAddCommGroup V
inst✝⁴ : NormedAddCommGroup V'
inst✝³ : InnerProductSpace ℝ V
inst✝² : InnerProductSpace ℝ V'
inst✝¹ : Fact (finrank ℝ V = 2)
inst✝ : Fact (finrank ℝ V' = 2)
o : Orientation ℝ V (Fin 2)
x y : V
r₁ r₂ r₃ r₄ : ℝ
⊢ Real.Angle.sign (oangle o (r₁ • x + r₂ • y) (r₃ • x + r₄ • y)) =
    SignType.sign (r₁ * r₄ - r₂ * r₃) * Real.Angle.sign (oangle o x y)

Next tactic:
by_cases hr₁ : r₁ = 0
/-- The sign of the angle between two linear combinations of two vectors is the sign of the
determinant of the factors in those combinations multiplied by the sign of the angle between the
two vectors. -/
theorem oangle_sign_smul_add_smul_smul_add_smul (x y : V) (r₁ r₂ r₃ r₄ : ℝ) :
    (o.oangle (r₁ • x + r₂ • y) (r₃ • x + r₄ • y)).sign =
      SignType.sign (r₁ * r₄ - r₂ * r₃) * (o.oangle x y).sign := by
  by_cases hr₁ : r₁ = 0
  · 

Proof state:
case pos
V : Type u_1
V' : Type u_2
inst✝⁵ : NormedAddCommGroup V
inst✝⁴ : NormedAddCommGroup V'
inst✝³ : InnerProductSpace ℝ V
inst✝² : InnerProductSpace ℝ V'
inst✝¹ : Fact (finrank ℝ V = 2)
inst✝ : Fact (finrank ℝ V' = 2)
o : Orientation ℝ V (Fin 2)
x y : V
r₁ r₂ r₃ r₄ : ℝ
hr₁ : r₁ = 0
⊢ Real.Angle.sign (oangle o (r₁ • x + r₂ • y) (r₃ • x + r₄ • y)) =
    SignType.sign (r₁ * r₄ - r₂ * r₃) * Real.Angle.sign (oangle o x y)

Next tactic:
rw [hr₁, zero_smul, zero_mul, zero_add, zero_sub, Left.sign_neg,
      oangle_sign_smul_left, add_comm, oangle_sign_smul_add_smul_right, oangle_rev,
      Real.Angle.sign_neg, sign_mul, mul_neg, mul_neg, neg_mul, mul_assoc]
/-- The sign of the angle between two linear combinations of two vectors is the sign of the
determinant of the factors in those combinations multiplied by the sign of the angle between the
two vectors. -/
theorem oangle_sign_smul_add_smul_smul_add_smul (x y : V) (r₁ r₂ r₃ r₄ : ℝ) :
    (o.oangle (r₁ • x + r₂ • y) (r₃ • x + r₄ • y)).sign =
      SignType.sign (r₁ * r₄ - r₂ * r₃) * (o.oangle x y).sign := by
  by_cases hr₁ : r₁ = 0
  · rw [hr₁, zero_smul, zero_mul, zero_add, zero_sub, Left.sign_neg,
      oangle_sign_smul_left, add_comm, oangle_sign_smul_add_smul_right, oangle_rev,
      Real.Angle.sign_neg, sign_mul, mul_neg, mul_neg, neg_mul, mul_assoc]
  · 

Proof state:
case neg
V : Type u_1
V' : Type u_2
inst✝⁵ : NormedAddCommGroup V
inst✝⁴ : NormedAddCommGroup V'
inst✝³ : InnerProductSpace ℝ V
inst✝² : InnerProductSpace ℝ V'
inst✝¹ : Fact (finrank ℝ V = 2)
inst✝ : Fact (finrank ℝ V' = 2)
o : Orientation ℝ V (Fin 2)
x y : V
r₁ r₂ r₃ r₄ : ℝ
hr₁ : ¬r₁ = 0
⊢ Real.Angle.sign (oangle o (r₁ • x + r₂ • y) (r₃ • x + r₄ • y)) =
    SignType.sign (r₁ * r₄ - r₂ * r₃) * Real.Angle.sign (oangle o x y)

Next tactic:
rw [← o.oangle_sign_smul_add_right (r₁ • x + r₂ • y) (r₃ • x + r₄ • y) (-r₃ / r₁), smul_add,
      smul_smul, smul_smul, div_mul_cancel _ hr₁, neg_smul, ← add_assoc, add_comm (-(r₃ • x)), ←
      sub_eq_add_neg, sub_add_cancel, ← add_smul, oangle_sign_smul_right,
      oangle_sign_smul_add_smul_left, ← mul_assoc, ← sign_mul, add_mul, mul_assoc, mul_comm r₂ r₁, ←
      mul_assoc, div_mul_cancel _ hr₁, add_comm, neg_mul, ← sub_eq_add_neg, mul_comm r₄,
      mul_comm r₃]
/-- A base angle of an isosceles triangle is acute, oriented vector angle form. -/
theorem abs_oangle_sub_left_toReal_lt_pi_div_two {x y : V} (h : ‖x‖ = ‖y‖) :
    |(o.oangle (y - x) y).toReal| < π / 2 := by
  

Proof state:
V : Type u_1
V' : Type u_2
inst✝⁵ : NormedAddCommGroup V
inst✝⁴ : NormedAddCommGroup V'
inst✝³ : InnerProductSpace ℝ V
inst✝² : InnerProductSpace ℝ V'
inst✝¹ : Fact (finrank ℝ V = 2)
inst✝ : Fact (finrank ℝ V' = 2)
o : Orientation ℝ V (Fin 2)
x y : V
h : ‖x‖ = ‖y‖
⊢ |Real.Angle.toReal (oangle o (y - x) y)| < π / 2

Next tactic:
by_cases hn : x = y
/-- A base angle of an isosceles triangle is acute, oriented vector angle form. -/
theorem abs_oangle_sub_left_toReal_lt_pi_div_two {x y : V} (h : ‖x‖ = ‖y‖) :
    |(o.oangle (y - x) y).toReal| < π / 2 := by
  by_cases hn : x = y; · 

Proof state:
case pos
V : Type u_1
V' : Type u_2
inst✝⁵ : NormedAddCommGroup V
inst✝⁴ : NormedAddCommGroup V'
inst✝³ : InnerProductSpace ℝ V
inst✝² : InnerProductSpace ℝ V'
inst✝¹ : Fact (finrank ℝ V = 2)
inst✝ : Fact (finrank ℝ V' = 2)
o : Orientation ℝ V (Fin 2)
x y : V
h : ‖x‖ = ‖y‖
hn : x = y
⊢ |Real.Angle.toReal (oangle o (y - x) y)| < π / 2

Next tactic:
simp [hn, div_pos, Real.pi_pos]
/-- A base angle of an isosceles triangle is acute, oriented vector angle form. -/
theorem abs_oangle_sub_left_toReal_lt_pi_div_two {x y : V} (h : ‖x‖ = ‖y‖) :
    |(o.oangle (y - x) y).toReal| < π / 2 := by
  by_cases hn : x = y; · simp [hn, div_pos, Real.pi_pos]
  

Proof state:
case neg
V : Type u_1
V' : Type u_2
inst✝⁵ : NormedAddCommGroup V
inst✝⁴ : NormedAddCommGroup V'
inst✝³ : InnerProductSpace ℝ V
inst✝² : InnerProductSpace ℝ V'
inst✝¹ : Fact (finrank ℝ V = 2)
inst✝ : Fact (finrank ℝ V' = 2)
o : Orientation ℝ V (Fin 2)
x y : V
h : ‖x‖ = ‖y‖
hn : ¬x = y
⊢ |Real.Angle.toReal (oangle o (y - x) y)| < π / 2

Next tactic:
have hs : ((2 : ℤ) • o.oangle (y - x) y).sign = (o.oangle (y - x) y).sign := by
    conv_rhs => rw [oangle_sign_sub_left_swap]
    rw [o.oangle_eq_pi_sub_two_zsmul_oangle_sub_of_norm_eq hn h, Real.Angle.sign_pi_sub]
/-- A base angle of an isosceles triangle is acute, oriented vector angle form. -/
theorem abs_oangle_sub_left_toReal_lt_pi_div_two {x y : V} (h : ‖x‖ = ‖y‖) :
    |(o.oangle (y - x) y).toReal| < π / 2 := by
  by_cases hn : x = y; · simp [hn, div_pos, Real.pi_pos]
  have hs : ((2 : ℤ) • o.oangle (y - x) y).sign = (o.oangle (y - x) y).sign := by
    

Proof state:
V : Type u_1
V' : Type u_2
inst✝⁵ : NormedAddCommGroup V
inst✝⁴ : NormedAddCommGroup V'
inst✝³ : InnerProductSpace ℝ V
inst✝² : InnerProductSpace ℝ V'
inst✝¹ : Fact (finrank ℝ V = 2)
inst✝ : Fact (finrank ℝ V' = 2)
o : Orientation ℝ V (Fin 2)
x y : V
h : ‖x‖ = ‖y‖
hn : ¬x = y
⊢ Real.Angle.sign (2 • oangle o (y - x) y) = Real.Angle.sign (oangle o (y - x) y)

Next tactic:
conv_rhs => rw [oangle_sign_sub_left_swap]
/-- A base angle of an isosceles triangle is acute, oriented vector angle form. -/
theorem abs_oangle_sub_left_toReal_lt_pi_div_two {x y : V} (h : ‖x‖ = ‖y‖) :
    |(o.oangle (y - x) y).toReal| < π / 2 := by
  by_cases hn : x = y; · simp [hn, div_pos, Real.pi_pos]
  have hs : ((2 : ℤ) • o.oangle (y - x) y).sign = (o.oangle (y - x) y).sign := by
    conv_rhs => 

Proof state:
V : Type u_1
V' : Type u_2
inst✝⁵ : NormedAddCommGroup V
inst✝⁴ : NormedAddCommGroup V'
inst✝³ : InnerProductSpace ℝ V
inst✝² : InnerProductSpace ℝ V'
inst✝¹ : Fact (finrank ℝ V = 2)
inst✝ : Fact (finrank ℝ V' = 2)
o : Orientation ℝ V (Fin 2)
x y : V
h : ‖x‖ = ‖y‖
hn : ¬x = y
| Real.Angle.sign (oangle o (y - x) y)

Next tactic:
rw [oangle_sign_sub_left_swap]
/-- A base angle of an isosceles triangle is acute, oriented vector angle form. -/
theorem abs_oangle_sub_left_toReal_lt_pi_div_two {x y : V} (h : ‖x‖ = ‖y‖) :
    |(o.oangle (y - x) y).toReal| < π / 2 := by
  by_cases hn : x = y; · simp [hn, div_pos, Real.pi_pos]
  have hs : ((2 : ℤ) • o.oangle (y - x) y).sign = (o.oangle (y - x) y).sign := by
    conv_rhs => rw [oangle_sign_sub_left_swap]
    

Proof state:
V : Type u_1
V' : Type u_2
inst✝⁵ : NormedAddCommGroup V
inst✝⁴ : NormedAddCommGroup V'
inst✝³ : InnerProductSpace ℝ V
inst✝² : InnerProductSpace ℝ V'
inst✝¹ : Fact (finrank ℝ V = 2)
inst✝ : Fact (finrank ℝ V' = 2)
o : Orientation ℝ V (Fin 2)
x y : V
h : ‖x‖ = ‖y‖
hn : ¬x = y
⊢ Real.Angle.sign (2 • oangle o (y - x) y) = Real.Angle.sign (oangle o y x)

Next tactic:
rw [o.oangle_eq_pi_sub_two_zsmul_oangle_sub_of_norm_eq hn h, Real.Angle.sign_pi_sub]
/-- A base angle of an isosceles triangle is acute, oriented vector angle form. -/
theorem abs_oangle_sub_left_toReal_lt_pi_div_two {x y : V} (h : ‖x‖ = ‖y‖) :
    |(o.oangle (y - x) y).toReal| < π / 2 := by
  by_cases hn : x = y; · simp [hn, div_pos, Real.pi_pos]
  have hs : ((2 : ℤ) • o.oangle (y - x) y).sign = (o.oangle (y - x) y).sign := by
    conv_rhs => rw [oangle_sign_sub_left_swap]
    rw [o.oangle_eq_pi_sub_two_zsmul_oangle_sub_of_norm_eq hn h, Real.Angle.sign_pi_sub]
  

Proof state:
case neg
V : Type u_1
V' : Type u_2
inst✝⁵ : NormedAddCommGroup V
inst✝⁴ : NormedAddCommGroup V'
inst✝³ : InnerProductSpace ℝ V
inst✝² : InnerProductSpace ℝ V'
inst✝¹ : Fact (finrank ℝ V = 2)
inst✝ : Fact (finrank ℝ V' = 2)
o : Orientation ℝ V (Fin 2)
x y : V
h : ‖x‖ = ‖y‖
hn : ¬x = y
hs : Real.Angle.sign (2 • oangle o (y - x) y) = Real.Angle.sign (oangle o (y - x) y)
⊢ |Real.Angle.toReal (oangle o (y - x) y)| < π / 2

Next tactic:
rw [Real.Angle.sign_two_zsmul_eq_sign_iff] at hs
/-- A base angle of an isosceles triangle is acute, oriented vector angle form. -/
theorem abs_oangle_sub_left_toReal_lt_pi_div_two {x y : V} (h : ‖x‖ = ‖y‖) :
    |(o.oangle (y - x) y).toReal| < π / 2 := by
  by_cases hn : x = y; · simp [hn, div_pos, Real.pi_pos]
  have hs : ((2 : ℤ) • o.oangle (y - x) y).sign = (o.oangle (y - x) y).sign := by
    conv_rhs => rw [oangle_sign_sub_left_swap]
    rw [o.oangle_eq_pi_sub_two_zsmul_oangle_sub_of_norm_eq hn h, Real.Angle.sign_pi_sub]
  rw [Real.Angle.sign_two_zsmul_eq_sign_iff] at hs
  

Proof state:
case neg
V : Type u_1
V' : Type u_2
inst✝⁵ : NormedAddCommGroup V
inst✝⁴ : NormedAddCommGroup V'
inst✝³ : InnerProductSpace ℝ V
inst✝² : InnerProductSpace ℝ V'
inst✝¹ : Fact (finrank ℝ V = 2)
inst✝ : Fact (finrank ℝ V' = 2)
o : Orientation ℝ V (Fin 2)
x y : V
h : ‖x‖ = ‖y‖
hn : ¬x = y
hs : oangle o (y - x) y = ↑π ∨ |Real.Angle.toReal (oangle o (y - x) y)| < π / 2
⊢ |Real.Angle.toReal (oangle o (y - x) y)| < π / 2

Next tactic:
rcases hs with (hs | hs)
/-- A base angle of an isosceles triangle is acute, oriented vector angle form. -/
theorem abs_oangle_sub_left_toReal_lt_pi_div_two {x y : V} (h : ‖x‖ = ‖y‖) :
    |(o.oangle (y - x) y).toReal| < π / 2 := by
  by_cases hn : x = y; · simp [hn, div_pos, Real.pi_pos]
  have hs : ((2 : ℤ) • o.oangle (y - x) y).sign = (o.oangle (y - x) y).sign := by
    conv_rhs => rw [oangle_sign_sub_left_swap]
    rw [o.oangle_eq_pi_sub_two_zsmul_oangle_sub_of_norm_eq hn h, Real.Angle.sign_pi_sub]
  rw [Real.Angle.sign_two_zsmul_eq_sign_iff] at hs
  rcases hs with (hs | hs)
  · 

Proof state:
case neg.inl
V : Type u_1
V' : Type u_2
inst✝⁵ : NormedAddCommGroup V
inst✝⁴ : NormedAddCommGroup V'
inst✝³ : InnerProductSpace ℝ V
inst✝² : InnerProductSpace ℝ V'
inst✝¹ : Fact (finrank ℝ V = 2)
inst✝ : Fact (finrank ℝ V' = 2)
o : Orientation ℝ V (Fin 2)
x y : V
h : ‖x‖ = ‖y‖
hn : ¬x = y
hs : oangle o (y - x) y = ↑π
⊢ |Real.Angle.toReal (oangle o (y - x) y)| < π / 2

Next tactic:
rw [oangle_eq_pi_iff_oangle_rev_eq_pi, oangle_eq_pi_iff_sameRay_neg, neg_sub] at hs
/-- A base angle of an isosceles triangle is acute, oriented vector angle form. -/
theorem abs_oangle_sub_left_toReal_lt_pi_div_two {x y : V} (h : ‖x‖ = ‖y‖) :
    |(o.oangle (y - x) y).toReal| < π / 2 := by
  by_cases hn : x = y; · simp [hn, div_pos, Real.pi_pos]
  have hs : ((2 : ℤ) • o.oangle (y - x) y).sign = (o.oangle (y - x) y).sign := by
    conv_rhs => rw [oangle_sign_sub_left_swap]
    rw [o.oangle_eq_pi_sub_two_zsmul_oangle_sub_of_norm_eq hn h, Real.Angle.sign_pi_sub]
  rw [Real.Angle.sign_two_zsmul_eq_sign_iff] at hs
  rcases hs with (hs | hs)
  · rw [oangle_eq_pi_iff_oangle_rev_eq_pi, oangle_eq_pi_iff_sameRay_neg, neg_sub] at hs
    

Proof state:
case neg.inl
V : Type u_1
V' : Type u_2
inst✝⁵ : NormedAddCommGroup V
inst✝⁴ : NormedAddCommGroup V'
inst✝³ : InnerProductSpace ℝ V
inst✝² : InnerProductSpace ℝ V'
inst✝¹ : Fact (finrank ℝ V = 2)
inst✝ : Fact (finrank ℝ V' = 2)
o : Orientation ℝ V (Fin 2)
x y : V
h : ‖x‖ = ‖y‖
hn : ¬x = y
hs : y ≠ 0 ∧ y - x ≠ 0 ∧ SameRay ℝ y (x - y)
⊢ |Real.Angle.toReal (oangle o (y - x) y)| < π / 2

Next tactic:
rcases hs with ⟨hy, -, hr⟩