-- Mathlib/AlgebraicGeometry/EllipticCurve/Affine.lean
/-- The negated addition of two nonsingular affine points in `W` on a sloped line is nonsingular. -/
lemma nonsingular_negAdd {x₁ x₂ y₁ y₂ : F} (h₁ : W.Nonsingular x₁ y₁) (h₂ : W.Nonsingular x₂ y₂)
    (hxy : ¬(x₁ = x₂ ∧ y₁ = W.negY x₂ y₂)) : W.Nonsingular
      (W.addX x₁ x₂ <| W.slope x₁ x₂ y₁ y₂) (W.negAddY x₁ x₂ y₁ <| W.slope x₁ x₂ y₁ y₂)

Proof state:
case neg
F : Type u
inst✝ : Field F
W : Affine F
x₁ x₂ y₁ y₂ : F
h₁ : W.Nonsingular x₁ y₁
h₂ : W.Nonsingular x₂ y₂
hxy : ¬(x₁ = x₂ ∧ y₁ = W.negY x₂ y₂)
hx₁ : ¬W.addX x₁ x₂ (W.slope x₁ x₂ y₁ y₂) = x₁
⊢ W.Nonsingular (W.addX x₁ x₂ (W.slope x₁ x₂ y₁ y₂)) (W.negAddY x₁ x₂ y₁ (W.slope x₁ x₂ y₁ y₂))

Tactic:
by_cases hx₂ : W.addX x₁ x₂ (W.slope x₁ x₂ y₁ y₂) = x₂

Result:
case pos
F : Type u
inst✝ : Field F
W : Affine F
x₁ x₂ y₁ y₂ : F
h₁ : W.Nonsingular x₁ y₁
h₂ : W.Nonsingular x₂ y₂
hxy : ¬(x₁ = x₂ ∧ y₁ = W.negY x₂ y₂)
hx₁ : ¬W.addX x₁ x₂ (W.slope x₁ x₂ y₁ y₂) = x₁
hx₂ : W.addX x₁ x₂ (W.slope x₁ x₂ y₁ y₂) = x₂
⊢ W.Nonsingular (W.addX x₁ x₂ (W.slope x₁ x₂ y₁ y₂)) (W.negAddY x₁ x₂ y₁ (W.slope x₁ x₂ y₁ y₂))

case neg
F : Type u
inst✝ : Field F
W : Affine F
x₁ x₂ y₁ y₂ : F
h₁ : W.Nonsingular x₁ y₁
h₂ : W.Nonsingular x₂ y₂
hxy : ¬(x₁ = x₂ ∧ y₁ = W.negY x₂ y₂)
hx₁ : ¬W.addX x₁ x₂ (W.slope x₁ x₂ y₁ y₂) = x₁
hx₂ : ¬W.addX x₁ x₂ (W.slope x₁ x₂ y₁ y₂) = x₂
⊢ W.Nonsingular (W.addX x₁ x₂ (W.slope x₁ x₂ y₁ y₂)) (W.negAddY x₁ x₂ y₁ (W.slope x₁ x₂ y₁ y₂))

Proof state:
case neg
F : Type u
inst✝ : Field F
W : Affine F
x₁ x₂ y₁ y₂ : F
h₁ : W.Nonsingular x₁ y₁
h₂ : W.Nonsingular x₂ y₂
hxy : ¬(x₁ = x₂ ∧ y₁ = W.negY x₂ y₂)
hx₁ : ¬W.addX x₁ x₂ (W.slope x₁ x₂ y₁ y₂) = x₁
hx₂ : W.addX x₁ x₂ (W.slope x₁ x₂ y₁ y₂) = x₂
hx : ¬x₁ = x₂
⊢ W.Nonsingular (W.addX x₁ x₂ (W.slope x₁ x₂ y₁ y₂)) (W.negAddY x₁ x₂ y₁ (W.slope x₁ x₂ y₁ y₂))

Tactic:
rwa [negAddY, ← neg_sub, mul_neg, hx₂, slope_of_X_ne hx,
  div_mul_cancel₀ _ <| sub_ne_zero_of_ne hx, neg_sub, sub_add_cancel]

Result:
no goals

Proof state:
case pos
F : Type u
inst✝ : Field F
W : Affine F
x₁ x₂ y₁ y₂ : F
h₁ : W.Nonsingular x₁ y₁
h₂ : W.Nonsingular x₂ y₂
hxy : ¬(x₁ = x₂ ∧ y₁ = W.negY x₂ y₂)
hx₁ : ¬W.addX x₁ x₂ (W.slope x₁ x₂ y₁ y₂) = x₁
hx₂ : W.addX x₁ x₂ (W.slope x₁ x₂ y₁ y₂) = x₂
hx : x₁ = x₂
⊢ W.Nonsingular (W.addX x₁ x₂ (W.slope x₁ x₂ y₁ y₂)) (W.negAddY x₁ x₂ y₁ (W.slope x₁ x₂ y₁ y₂))

Tactic:
subst hx

Result:
case pos
F : Type u
inst✝ : Field F
W : Affine F
x₁ y₁ y₂ : F
h₁ : W.Nonsingular x₁ y₁
h₂ : W.Nonsingular x₁ y₂
hxy : ¬(x₁ = x₁ ∧ y₁ = W.negY x₁ y₂)
hx₁ : ¬W.addX x₁ x₁ (W.slope x₁ x₁ y₁ y₂) = x₁
hx₂ : W.addX x₁ x₁ (W.slope x₁ x₁ y₁ y₂) = x₁
⊢ W.Nonsingular (W.addX x₁ x₁ (W.slope x₁ x₁ y₁ y₂)) (W.negAddY x₁ x₁ y₁ (W.slope x₁ x₁ y₁ y₂))

Proof state:
case pos
F : Type u
inst✝ : Field F
W : Affine F
x₁ y₁ y₂ : F
h₁ : W.Nonsingular x₁ y₁
h₂ : W.Nonsingular x₁ y₂
hxy : ¬(x₁ = x₁ ∧ y₁ = W.negY x₁ y₂)
hx₁ : ¬W.addX x₁ x₁ (W.slope x₁ x₁ y₁ y₂) = x₁
hx₂ : W.addX x₁ x₁ (W.slope x₁ x₁ y₁ y₂) = x₁
⊢ W.Nonsingular (W.addX x₁ x₁ (W.slope x₁ x₁ y₁ y₂)) (W.negAddY x₁ x₁ y₁ (W.slope x₁ x₁ y₁ y₂))

Tactic:
contradiction

Result:
no goals

Proof state:
case pos
F : Type u
inst✝ : Field F
W : Affine F
x₁ x₂ y₁ y₂ : F
h₁ : W.Nonsingular x₁ y₁
h₂ : W.Nonsingular x₂ y₂
hxy : ¬(x₁ = x₂ ∧ y₁ = W.negY x₂ y₂)
hx₁ : ¬W.addX x₁ x₂ (W.slope x₁ x₂ y₁ y₂) = x₁
hx₂ : W.addX x₁ x₂ (W.slope x₁ x₂ y₁ y₂) = x₂
⊢ W.Nonsingular (W.addX x₁ x₂ (W.slope x₁ x₂ y₁ y₂)) (W.negAddY x₁ x₂ y₁ (W.slope x₁ x₂ y₁ y₂))

Tactic:
by_cases hx : x₁ = x₂

Result:
case pos
F : Type u
inst✝ : Field F
W : Affine F
x₁ x₂ y₁ y₂ : F
h₁ : W.Nonsingular x₁ y₁
h₂ : W.Nonsingular x₂ y₂
hxy : ¬(x₁ = x₂ ∧ y₁ = W.negY x₂ y₂)
hx₁ : ¬W.addX x₁ x₂ (W.slope x₁ x₂ y₁ y₂) = x₁
hx₂ : W.addX x₁ x₂ (W.slope x₁ x₂ y₁ y₂) = x₂
hx : x₁ = x₂
⊢ W.Nonsingular (W.addX x₁ x₂ (W.slope x₁ x₂ y₁ y₂)) (W.negAddY x₁ x₂ y₁ (W.slope x₁ x₂ y₁ y₂))

case neg
F : Type u
inst✝ : Field F
W : Affine F
x₁ x₂ y₁ y₂ : F
h₁ : W.Nonsingular x₁ y₁
h₂ : W.Nonsingular x₂ y₂
hxy : ¬(x₁ = x₂ ∧ y₁ = W.negY x₂ y₂)
hx₁ : ¬W.addX x₁ x₂ (W.slope x₁ x₂ y₁ y₂) = x₁
hx₂ : W.addX x₁ x₂ (W.slope x₁ x₂ y₁ y₂) = x₂
hx : ¬x₁ = x₂
⊢ W.Nonsingular (W.addX x₁ x₂ (W.slope x₁ x₂ y₁ y₂)) (W.negAddY x₁ x₂ y₁ (W.slope x₁ x₂ y₁ y₂))

Proof state:
F : Type u
inst✝ : Field F
W : Affine F
x₁ x₂ y₁ y₂ : F
h₁ : W.Nonsingular x₁ y₁
h₂ : W.Nonsingular x₂ y₂
hxy : ¬(x₁ = x₂ ∧ y₁ = W.negY x₂ y₂)
⊢ W.Nonsingular (W.addX x₁ x₂ (W.slope x₁ x₂ y₁ y₂)) (W.negAddY x₁ x₂ y₁ (W.slope x₁ x₂ y₁ y₂))

Tactic:
by_cases hx₁ : W.addX x₁ x₂ (W.slope x₁ x₂ y₁ y₂) = x₁

Result:
case pos
F : Type u
inst✝ : Field F
W : Affine F
x₁ x₂ y₁ y₂ : F
h₁ : W.Nonsingular x₁ y₁
h₂ : W.Nonsingular x₂ y₂
hxy : ¬(x₁ = x₂ ∧ y₁ = W.negY x₂ y₂)
hx₁ : W.addX x₁ x₂ (W.slope x₁ x₂ y₁ y₂) = x₁
⊢ W.Nonsingular (W.addX x₁ x₂ (W.slope x₁ x₂ y₁ y₂)) (W.negAddY x₁ x₂ y₁ (W.slope x₁ x₂ y₁ y₂))

case neg
F : Type u
inst✝ : Field F
W : Affine F
x₁ x₂ y₁ y₂ : F
h₁ : W.Nonsingular x₁ y₁
h₂ : W.Nonsingular x₂ y₂
hxy : ¬(x₁ = x₂ ∧ y₁ = W.negY x₂ y₂)
hx₁ : ¬W.addX x₁ x₂ (W.slope x₁ x₂ y₁ y₂) = x₁
⊢ W.Nonsingular (W.addX x₁ x₂ (W.slope x₁ x₂ y₁ y₂)) (W.negAddY x₁ x₂ y₁ (W.slope x₁ x₂ y₁ y₂))

Proof state:
case neg
F : Type u
inst✝ : Field F
W : Affine F
x₁ x₂ y₁ y₂ : F
h₁ : W.Nonsingular x₁ y₁
h₂ : W.Nonsingular x₂ y₂
hxy : ¬(x₁ = x₂ ∧ y₁ = W.negY x₂ y₂)
hx₁ : ¬W.addX x₁ x₂ (W.slope x₁ x₂ y₁ y₂) = x₁
hx₂ : ¬W.addX x₁ x₂ (W.slope x₁ x₂ y₁ y₂) = x₂
⊢ (W.addX x₁ x₂ (W.slope x₁ x₂ y₁ y₂) - x₁) * (W.addX x₁ x₂ (W.slope x₁ x₂ y₁ y₂) - x₂) ≠ 0

Tactic:
exact mul_ne_zero (sub_ne_zero_of_ne hx₁) (sub_ne_zero_of_ne hx₂)

Result:
no goals

Proof state:
case neg
F : Type u
inst✝ : Field F
W : Affine F
x₁ x₂ y₁ y₂ : F
h₁ : W.Nonsingular x₁ y₁
h₂ : W.Nonsingular x₂ y₂
hxy : ¬(x₁ = x₂ ∧ y₁ = W.negY x₂ y₂)
hx₁ : ¬W.addX x₁ x₂ (W.slope x₁ x₂ y₁ y₂) = x₁
hx₂ : ¬W.addX x₁ x₂ (W.slope x₁ x₂ y₁ y₂) = x₂
⊢ eval (W.addX x₁ x₂ (W.slope x₁ x₂ y₁ y₂)) (derivative (W.addPolynomial x₁ y₁ (W.slope x₁ x₂ y₁ y₂))) ≠ 0

Tactic:
rw [derivative_addPolynomial_slope h₁.left h₂.left hxy]

Result:
case neg
F : Type u
inst✝ : Field F
W : Affine F
x₁ x₂ y₁ y₂ : F
h₁ : W.Nonsingular x₁ y₁
h₂ : W.Nonsingular x₂ y₂
hxy : ¬(x₁ = x₂ ∧ y₁ = W.negY x₂ y₂)
hx₁ : ¬W.addX x₁ x₂ (W.slope x₁ x₂ y₁ y₂) = x₁
hx₂ : ¬W.addX x₁ x₂ (W.slope x₁ x₂ y₁ y₂) = x₂
⊢ eval (W.addX x₁ x₂ (W.slope x₁ x₂ y₁ y₂))
      (-((X - C x₁) * (X - C x₂) + (X - C x₁) * (X - C (W.addX x₁ x₂ (W.slope x₁ x₂ y₁ y₂))) +
          (X - C x₂) * (X - C (W.addX x₁ x₂ (W.slope x₁ x₂ y₁ y₂))))) ≠
    0

Proof state:
case pos
F : Type u
inst✝ : Field F
W : Affine F
x₁ x₂ y₁ y₂ : F
h₁ : W.Nonsingular x₁ y₁
h₂ : W.Nonsingular x₂ y₂
hxy : ¬(x₁ = x₂ ∧ y₁ = W.negY x₂ y₂)
hx₁ : W.addX x₁ x₂ (W.slope x₁ x₂ y₁ y₂) = x₁
⊢ W.Nonsingular (W.addX x₁ x₂ (W.slope x₁ x₂ y₁ y₂)) (W.negAddY x₁ x₂ y₁ (W.slope x₁ x₂ y₁ y₂))

Tactic:
rwa [negAddY, hx₁, sub_self, mul_zero, zero_add]

Result:
no goals

Proof state:
case neg
F : Type u
inst✝ : Field F
W : Affine F
x₁ x₂ y₁ y₂ : F
h₁ : W.Nonsingular x₁ y₁
h₂ : W.Nonsingular x₂ y₂
hxy : ¬(x₁ = x₂ ∧ y₁ = W.negY x₂ y₂)
hx₁ : ¬W.addX x₁ x₂ (W.slope x₁ x₂ y₁ y₂) = x₁
hx₂ : ¬W.addX x₁ x₂ (W.slope x₁ x₂ y₁ y₂) = x₂
⊢ eval (W.addX x₁ x₂ (W.slope x₁ x₂ y₁ y₂))
      (-((X - C x₁) * (X - C x₂) + (X - C x₁) * (X - C (W.addX x₁ x₂ (W.slope x₁ x₂ y₁ y₂))) +
          (X - C x₂) * (X - C (W.addX x₁ x₂ (W.slope x₁ x₂ y₁ y₂))))) ≠
    0

Tactic:
eval_simp

Result:
case neg
F : Type u
inst✝ : Field F
W : Affine F
x₁ x₂ y₁ y₂ : F
h₁ : W.Nonsingular x₁ y₁
h₂ : W.Nonsingular x₂ y₂
hxy : ¬(x₁ = x₂ ∧ y₁ = W.negY x₂ y₂)
hx₁ : ¬W.addX x₁ x₂ (W.slope x₁ x₂ y₁ y₂) = x₁
hx₂ : ¬W.addX x₁ x₂ (W.slope x₁ x₂ y₁ y₂) = x₂
⊢ -((W.addX x₁ x₂ (W.slope x₁ x₂ y₁ y₂) - x₁) * (W.addX x₁ x₂ (W.slope x₁ x₂ y₁ y₂) - x₂) +
          (W.addX x₁ x₂ (W.slope x₁ x₂ y₁ y₂) - x₁) *
            (W.addX x₁ x₂ (W.slope x₁ x₂ y₁ y₂) - W.addX x₁ x₂ (W.slope x₁ x₂ y₁ y₂)) +
        (W.addX x₁ x₂ (W.slope x₁ x₂ y₁ y₂) - x₂) *
          (W.addX x₁ x₂ (W.slope x₁ x₂ y₁ y₂) - W.addX x₁ x₂ (W.slope x₁ x₂ y₁ y₂))) ≠
    0