[GOAL]
V : Type u_1
inst✝³ : NormedAddCommGroup V
inst✝² : InnerProductSpace ℝ V
P : Type u_2
inst✝¹ : MetricSpace P
inst✝ : NormedAddTorsor V P
a b c d p : P
h : Cospherical {a, b, c, d}
hapc : ∠ a p c = π
hbpd : ∠ b p d = π
⊢ dist a b * dist c d + dist b c * dist d a = dist a c * dist b d
[PROOFSTEP]
have h' : Cospherical ({ a, c, b, d } : Set P) := by rwa [Set.insert_comm c b { d }]
[GOAL]
V : Type u_1
inst✝³ : NormedAddCommGroup V
inst✝² : InnerProductSpace ℝ V
P : Type u_2
inst✝¹ : MetricSpace P
inst✝ : NormedAddTorsor V P
a b c d p : P
h : Cospherical {a, b, c, d}
hapc : ∠ a p c = π
hbpd : ∠ b p d = π
⊢ Cospherical {a, c, b, d}
[PROOFSTEP]
rwa [Set.insert_comm c b { d }]
[GOAL]
V : Type u_1
inst✝³ : NormedAddCommGroup V
inst✝² : InnerProductSpace ℝ V
P : Type u_2
inst✝¹ : MetricSpace P
inst✝ : NormedAddTorsor V P
a b c d p : P
h : Cospherical {a, b, c, d}
hapc : ∠ a p c = π
hbpd : ∠ b p d = π
h' : Cospherical {a, c, b, d}
⊢ dist a b * dist c d + dist b c * dist d a = dist a c * dist b d
[PROOFSTEP]
have hmul := mul_dist_eq_mul_dist_of_cospherical_of_angle_eq_pi h' hapc hbpd
[GOAL]
V : Type u_1
inst✝³ : NormedAddCommGroup V
inst✝² : InnerProductSpace ℝ V
P : Type u_2
inst✝¹ : MetricSpace P
inst✝ : NormedAddTorsor V P
a b c d p : P
h : Cospherical {a, b, c, d}
hapc : ∠ a p c = π
hbpd : ∠ b p d = π
h' : Cospherical {a, c, b, d}
hmul : dist a p * dist c p = dist b p * dist d p
⊢ dist a b * dist c d + dist b c * dist d a = dist a c * dist b d
[PROOFSTEP]
have hbp := left_dist_ne_zero_of_angle_eq_pi hbpd
[GOAL]
V : Type u_1
inst✝³ : NormedAddCommGroup V
inst✝² : InnerProductSpace ℝ V
P : Type u_2
inst✝¹ : MetricSpace P
inst✝ : NormedAddTorsor V P
a b c d p : P
h : Cospherical {a, b, c, d}
hapc : ∠ a p c = π
hbpd : ∠ b p d = π
h' : Cospherical {a, c, b, d}
hmul : dist a p * dist c p = dist b p * dist d p
hbp : dist b p ≠ 0
⊢ dist a b * dist c d + dist b c * dist d a = dist a c * dist b d
[PROOFSTEP]
have h₁ : dist c d = dist c p / dist b p * dist a b :=
  by
  rw [dist_mul_of_eq_angle_of_dist_mul b p a c p d, dist_comm a b]
  · rw [angle_eq_angle_of_angle_eq_pi_of_angle_eq_pi hbpd hapc, angle_comm]
  all_goals field_simp [mul_comm, hmul]
[GOAL]
V : Type u_1
inst✝³ : NormedAddCommGroup V
inst✝² : InnerProductSpace ℝ V
P : Type u_2
inst✝¹ : MetricSpace P
inst✝ : NormedAddTorsor V P
a b c d p : P
h : Cospherical {a, b, c, d}
hapc : ∠ a p c = π
hbpd : ∠ b p d = π
h' : Cospherical {a, c, b, d}
hmul : dist a p * dist c p = dist b p * dist d p
hbp : dist b p ≠ 0
⊢ dist c d = dist c p / dist b p * dist a b
[PROOFSTEP]
rw [dist_mul_of_eq_angle_of_dist_mul b p a c p d, dist_comm a b]
[GOAL]
case h
V : Type u_1
inst✝³ : NormedAddCommGroup V
inst✝² : InnerProductSpace ℝ V
P : Type u_2
inst✝¹ : MetricSpace P
inst✝ : NormedAddTorsor V P
a b c d p : P
h : Cospherical {a, b, c, d}
hapc : ∠ a p c = π
hbpd : ∠ b p d = π
h' : Cospherical {a, c, b, d}
hmul : dist a p * dist c p = dist b p * dist d p
hbp : dist b p ≠ 0
⊢ ∠ c p d = ∠ b p a
[PROOFSTEP]
rw [angle_eq_angle_of_angle_eq_pi_of_angle_eq_pi hbpd hapc, angle_comm]
[GOAL]
case hab
V : Type u_1
inst✝³ : NormedAddCommGroup V
inst✝² : InnerProductSpace ℝ V
P : Type u_2
inst✝¹ : MetricSpace P
inst✝ : NormedAddTorsor V P
a b c d p : P
h : Cospherical {a, b, c, d}
hapc : ∠ a p c = π
hbpd : ∠ b p d = π
h' : Cospherical {a, c, b, d}
hmul : dist a p * dist c p = dist b p * dist d p
hbp : dist b p ≠ 0
⊢ dist c p = dist c p / dist b p * dist b p
case hcb
V : Type u_1
inst✝³ : NormedAddCommGroup V
inst✝² : InnerProductSpace ℝ V
P : Type u_2
inst✝¹ : MetricSpace P
inst✝ : NormedAddTorsor V P
a b c d p : P
h : Cospherical {a, b, c, d}
hapc : ∠ a p c = π
hbpd : ∠ b p d = π
h' : Cospherical {a, c, b, d}
hmul : dist a p * dist c p = dist b p * dist d p
hbp : dist b p ≠ 0
⊢ dist d p = dist c p / dist b p * dist a p
[PROOFSTEP]
all_goals field_simp [mul_comm, hmul]
[GOAL]
case hab
V : Type u_1
inst✝³ : NormedAddCommGroup V
inst✝² : InnerProductSpace ℝ V
P : Type u_2
inst✝¹ : MetricSpace P
inst✝ : NormedAddTorsor V P
a b c d p : P
h : Cospherical {a, b, c, d}
hapc : ∠ a p c = π
hbpd : ∠ b p d = π
h' : Cospherical {a, c, b, d}
hmul : dist a p * dist c p = dist b p * dist d p
hbp : dist b p ≠ 0
⊢ dist c p = dist c p / dist b p * dist b p
[PROOFSTEP]
field_simp [mul_comm, hmul]
[GOAL]
case hcb
V : Type u_1
inst✝³ : NormedAddCommGroup V
inst✝² : InnerProductSpace ℝ V
P : Type u_2
inst✝¹ : MetricSpace P
inst✝ : NormedAddTorsor V P
a b c d p : P
h : Cospherical {a, b, c, d}
hapc : ∠ a p c = π
hbpd : ∠ b p d = π
h' : Cospherical {a, c, b, d}
hmul : dist a p * dist c p = dist b p * dist d p
hbp : dist b p ≠ 0
⊢ dist d p = dist c p / dist b p * dist a p
[PROOFSTEP]
field_simp [mul_comm, hmul]
[GOAL]
V : Type u_1
inst✝³ : NormedAddCommGroup V
inst✝² : InnerProductSpace ℝ V
P : Type u_2
inst✝¹ : MetricSpace P
inst✝ : NormedAddTorsor V P
a b c d p : P
h : Cospherical {a, b, c, d}
hapc : ∠ a p c = π
hbpd : ∠ b p d = π
h' : Cospherical {a, c, b, d}
hmul : dist a p * dist c p = dist b p * dist d p
hbp : dist b p ≠ 0
h₁ : dist c d = dist c p / dist b p * dist a b
⊢ dist a b * dist c d + dist b c * dist d a = dist a c * dist b d
[PROOFSTEP]
have h₂ : dist d a = dist a p / dist b p * dist b c :=
  by
  rw [dist_mul_of_eq_angle_of_dist_mul c p b d p a, dist_comm c b]
  · rwa [angle_comm, angle_eq_angle_of_angle_eq_pi_of_angle_eq_pi]; rwa [angle_comm]
  all_goals field_simp [mul_comm, hmul]
[GOAL]
V : Type u_1
inst✝³ : NormedAddCommGroup V
inst✝² : InnerProductSpace ℝ V
P : Type u_2
inst✝¹ : MetricSpace P
inst✝ : NormedAddTorsor V P
a b c d p : P
h : Cospherical {a, b, c, d}
hapc : ∠ a p c = π
hbpd : ∠ b p d = π
h' : Cospherical {a, c, b, d}
hmul : dist a p * dist c p = dist b p * dist d p
hbp : dist b p ≠ 0
h₁ : dist c d = dist c p / dist b p * dist a b
⊢ dist d a = dist a p / dist b p * dist b c
[PROOFSTEP]
rw [dist_mul_of_eq_angle_of_dist_mul c p b d p a, dist_comm c b]
[GOAL]
case h
V : Type u_1
inst✝³ : NormedAddCommGroup V
inst✝² : InnerProductSpace ℝ V
P : Type u_2
inst✝¹ : MetricSpace P
inst✝ : NormedAddTorsor V P
a b c d p : P
h : Cospherical {a, b, c, d}
hapc : ∠ a p c = π
hbpd : ∠ b p d = π
h' : Cospherical {a, c, b, d}
hmul : dist a p * dist c p = dist b p * dist d p
hbp : dist b p ≠ 0
h₁ : dist c d = dist c p / dist b p * dist a b
⊢ ∠ d p a = ∠ c p b
[PROOFSTEP]
rwa [angle_comm, angle_eq_angle_of_angle_eq_pi_of_angle_eq_pi]
[GOAL]
case h.hbpd
V : Type u_1
inst✝³ : NormedAddCommGroup V
inst✝² : InnerProductSpace ℝ V
P : Type u_2
inst✝¹ : MetricSpace P
inst✝ : NormedAddTorsor V P
a b c d p : P
h : Cospherical {a, b, c, d}
hapc : ∠ a p c = π
hbpd : ∠ b p d = π
h' : Cospherical {a, c, b, d}
hmul : dist a p * dist c p = dist b p * dist d p
hbp : dist b p ≠ 0
h₁ : dist c d = dist c p / dist b p * dist a b
⊢ ∠ d p b = π
[PROOFSTEP]
rwa [angle_comm]
[GOAL]
case hab
V : Type u_1
inst✝³ : NormedAddCommGroup V
inst✝² : InnerProductSpace ℝ V
P : Type u_2
inst✝¹ : MetricSpace P
inst✝ : NormedAddTorsor V P
a b c d p : P
h : Cospherical {a, b, c, d}
hapc : ∠ a p c = π
hbpd : ∠ b p d = π
h' : Cospherical {a, c, b, d}
hmul : dist a p * dist c p = dist b p * dist d p
hbp : dist b p ≠ 0
h₁ : dist c d = dist c p / dist b p * dist a b
⊢ dist d p = dist a p / dist b p * dist c p
case hcb
V : Type u_1
inst✝³ : NormedAddCommGroup V
inst✝² : InnerProductSpace ℝ V
P : Type u_2
inst✝¹ : MetricSpace P
inst✝ : NormedAddTorsor V P
a b c d p : P
h : Cospherical {a, b, c, d}
hapc : ∠ a p c = π
hbpd : ∠ b p d = π
h' : Cospherical {a, c, b, d}
hmul : dist a p * dist c p = dist b p * dist d p
hbp : dist b p ≠ 0
h₁ : dist c d = dist c p / dist b p * dist a b
⊢ dist a p = dist a p / dist b p * dist b p
[PROOFSTEP]
all_goals field_simp [mul_comm, hmul]
[GOAL]
case hab
V : Type u_1
inst✝³ : NormedAddCommGroup V
inst✝² : InnerProductSpace ℝ V
P : Type u_2
inst✝¹ : MetricSpace P
inst✝ : NormedAddTorsor V P
a b c d p : P
h : Cospherical {a, b, c, d}
hapc : ∠ a p c = π
hbpd : ∠ b p d = π
h' : Cospherical {a, c, b, d}
hmul : dist a p * dist c p = dist b p * dist d p
hbp : dist b p ≠ 0
h₁ : dist c d = dist c p / dist b p * dist a b
⊢ dist d p = dist a p / dist b p * dist c p
[PROOFSTEP]
field_simp [mul_comm, hmul]
[GOAL]
case hcb
V : Type u_1
inst✝³ : NormedAddCommGroup V
inst✝² : InnerProductSpace ℝ V
P : Type u_2
inst✝¹ : MetricSpace P
inst✝ : NormedAddTorsor V P
a b c d p : P
h : Cospherical {a, b, c, d}
hapc : ∠ a p c = π
hbpd : ∠ b p d = π
h' : Cospherical {a, c, b, d}
hmul : dist a p * dist c p = dist b p * dist d p
hbp : dist b p ≠ 0
h₁ : dist c d = dist c p / dist b p * dist a b
⊢ dist a p = dist a p / dist b p * dist b p
[PROOFSTEP]
field_simp [mul_comm, hmul]
[GOAL]
V : Type u_1
inst✝³ : NormedAddCommGroup V
inst✝² : InnerProductSpace ℝ V
P : Type u_2
inst✝¹ : MetricSpace P
inst✝ : NormedAddTorsor V P
a b c d p : P
h : Cospherical {a, b, c, d}
hapc : ∠ a p c = π
hbpd : ∠ b p d = π
h' : Cospherical {a, c, b, d}
hmul : dist a p * dist c p = dist b p * dist d p
hbp : dist b p ≠ 0
h₁ : dist c d = dist c p / dist b p * dist a b
h₂ : dist d a = dist a p / dist b p * dist b c
⊢ dist a b * dist c d + dist b c * dist d a = dist a c * dist b d
[PROOFSTEP]
have h₃ : dist d p = dist a p * dist c p / dist b p := by field_simp [mul_comm, hmul]
[GOAL]
V : Type u_1
inst✝³ : NormedAddCommGroup V
inst✝² : InnerProductSpace ℝ V
P : Type u_2
inst✝¹ : MetricSpace P
inst✝ : NormedAddTorsor V P
a b c d p : P
h : Cospherical {a, b, c, d}
hapc : ∠ a p c = π
hbpd : ∠ b p d = π
h' : Cospherical {a, c, b, d}
hmul : dist a p * dist c p = dist b p * dist d p
hbp : dist b p ≠ 0
h₁ : dist c d = dist c p / dist b p * dist a b
h₂ : dist d a = dist a p / dist b p * dist b c
⊢ dist d p = dist a p * dist c p / dist b p
[PROOFSTEP]
field_simp [mul_comm, hmul]
[GOAL]
V : Type u_1
inst✝³ : NormedAddCommGroup V
inst✝² : InnerProductSpace ℝ V
P : Type u_2
inst✝¹ : MetricSpace P
inst✝ : NormedAddTorsor V P
a b c d p : P
h : Cospherical {a, b, c, d}
hapc : ∠ a p c = π
hbpd : ∠ b p d = π
h' : Cospherical {a, c, b, d}
hmul : dist a p * dist c p = dist b p * dist d p
hbp : dist b p ≠ 0
h₁ : dist c d = dist c p / dist b p * dist a b
h₂ : dist d a = dist a p / dist b p * dist b c
h₃ : dist d p = dist a p * dist c p / dist b p
⊢ dist a b * dist c d + dist b c * dist d a = dist a c * dist b d
[PROOFSTEP]
have h₄ : ∀ x y : ℝ, x * (y * x) = x * x * y := fun x y => by rw [mul_left_comm, mul_comm]
[GOAL]
V : Type u_1
inst✝³ : NormedAddCommGroup V
inst✝² : InnerProductSpace ℝ V
P : Type u_2
inst✝¹ : MetricSpace P
inst✝ : NormedAddTorsor V P
a b c d p : P
h : Cospherical {a, b, c, d}
hapc : ∠ a p c = π
hbpd : ∠ b p d = π
h' : Cospherical {a, c, b, d}
hmul : dist a p * dist c p = dist b p * dist d p
hbp : dist b p ≠ 0
h₁ : dist c d = dist c p / dist b p * dist a b
h₂ : dist d a = dist a p / dist b p * dist b c
h₃ : dist d p = dist a p * dist c p / dist b p
x y : ℝ
⊢ x * (y * x) = x * x * y
[PROOFSTEP]
rw [mul_left_comm, mul_comm]
[GOAL]
V : Type u_1
inst✝³ : NormedAddCommGroup V
inst✝² : InnerProductSpace ℝ V
P : Type u_2
inst✝¹ : MetricSpace P
inst✝ : NormedAddTorsor V P
a b c d p : P
h : Cospherical {a, b, c, d}
hapc : ∠ a p c = π
hbpd : ∠ b p d = π
h' : Cospherical {a, c, b, d}
hmul : dist a p * dist c p = dist b p * dist d p
hbp : dist b p ≠ 0
h₁ : dist c d = dist c p / dist b p * dist a b
h₂ : dist d a = dist a p / dist b p * dist b c
h₃ : dist d p = dist a p * dist c p / dist b p
h₄ : ∀ (x y : ℝ), x * (y * x) = x * x * y
⊢ dist a b * dist c d + dist b c * dist d a = dist a c * dist b d
[PROOFSTEP]
field_simp [h₁, h₂, dist_eq_add_dist_of_angle_eq_pi hbpd, h₃, hbp, dist_comm a b, h₄, ← sq,
  dist_sq_mul_dist_add_dist_sq_mul_dist b, hapc]
