-- Mathlib/RingTheory/ClassGroup.lean
theorem ClassGroup.mk0_eq_mk0_iff [IsDedekindDomain R] {I J : (Ideal R)⁰} :
    ClassGroup.mk0 I = ClassGroup.mk0 J ↔
      ∃ (x y : R) (_hx : x ≠ 0) (_hy : y ≠ 0), Ideal.span {x} * (I : Ideal R) =
      Ideal.span {y} * J

Proof state:
case refine_1.intro.intro.intro.intro.mk.refine_2
R : Type u_1
inst✝² : CommRing R
inst✝¹ : IsDomain R
inst✝ : IsDedekindDomain R
I J : ↥(Ideal R)⁰
x y : R
hy : y ∈ R⁰
hz : mk' (FractionRing R) x ⟨y, hy⟩ ≠ 0
h : spanSingleton R⁰ (mk' (FractionRing R) x ⟨y, hy⟩) * ↑↑I = ↑↑J
⊢ Ideal.span {x} * ↑I = Ideal.span {y} * ↑J

Tactic:
exact (FractionalIdeal.mk'_mul_coeIdeal_eq_coeIdeal _ hy).mp h

Result:
no goals

Proof state:
case refine_2.intro.intro.intro.intro
R : Type u_1
inst✝² : CommRing R
inst✝¹ : IsDomain R
inst✝ : IsDedekindDomain R
I J : ↥(Ideal R)⁰
x y : R
hx : x ≠ 0
hy : y ≠ 0
h : Ideal.span {x} * ↑I = Ideal.span {y} * ↑J
⊢ ∃ x, ∃ (_ : x ≠ 0), spanSingleton R⁰ x * ↑↑I = ↑↑J

Tactic:
have hy' : y ∈ R⁰ := mem_nonZeroDivisors_iff_ne_zero.mpr hy

Result:
case refine_2.intro.intro.intro.intro
R : Type u_1
inst✝² : CommRing R
inst✝¹ : IsDomain R
inst✝ : IsDedekindDomain R
I J : ↥(Ideal R)⁰
x y : R
hx : x ≠ 0
hy : y ≠ 0
h : Ideal.span {x} * ↑I = Ideal.span {y} * ↑J
hy' : y ∈ R⁰
⊢ ∃ x, ∃ (_ : x ≠ 0), spanSingleton R⁰ x * ↑↑I = ↑↑J

Proof state:
case refine_2.intro.intro.intro.intro.refine_2
R : Type u_1
inst✝² : CommRing R
inst✝¹ : IsDomain R
inst✝ : IsDedekindDomain R
I J : ↥(Ideal R)⁰
x y : R
hx : x ≠ 0
hy : y ≠ 0
h : Ideal.span {x} * ↑I = Ideal.span {y} * ↑J
hy' : y ∈ R⁰
⊢ spanSingleton R⁰ (mk' (FractionRing R) x ⟨y, hy'⟩) * ↑↑I = ↑↑J

Tactic:
exact (FractionalIdeal.mk'_mul_coeIdeal_eq_coeIdeal _ hy').mpr h

Result:
no goals

Proof state:
case refine_1.intro.intro.intro.intro.mk.refine_1
R : Type u_1
inst✝² : CommRing R
inst✝¹ : IsDomain R
inst✝ : IsDedekindDomain R
I J : ↥(Ideal R)⁰
x y : R
hy : y ∈ R⁰
hz : mk' (FractionRing R) x ⟨y, hy⟩ ≠ 0
h : spanSingleton R⁰ (mk' (FractionRing R) x ⟨y, hy⟩) * ↑↑I = ↑↑J
⊢ x ≠ 0

Tactic:
rintro hx

Result:
case refine_1.intro.intro.intro.intro.mk.refine_1
R : Type u_1
inst✝² : CommRing R
inst✝¹ : IsDomain R
inst✝ : IsDedekindDomain R
I J : ↥(Ideal R)⁰
x y : R
hy : y ∈ R⁰
hz : mk' (FractionRing R) x ⟨y, hy⟩ ≠ 0
h : spanSingleton R⁰ (mk' (FractionRing R) x ⟨y, hy⟩) * ↑↑I = ↑↑J
hx : x = 0
⊢ False

Proof state:
case refine_1.intro.intro.intro.intro.mk.refine_1
R : Type u_1
inst✝² : CommRing R
inst✝¹ : IsDomain R
inst✝ : IsDedekindDomain R
I J : ↥(Ideal R)⁰
x y : R
hy : y ∈ R⁰
hz : mk' (FractionRing R) x ⟨y, hy⟩ ≠ 0
h : spanSingleton R⁰ (mk' (FractionRing R) x ⟨y, hy⟩) * ↑↑I = ↑↑J
hx : x = 0
⊢ False

Tactic:
apply hz

Result:
case refine_1.intro.intro.intro.intro.mk.refine_1
R : Type u_1
inst✝² : CommRing R
inst✝¹ : IsDomain R
inst✝ : IsDedekindDomain R
I J : ↥(Ideal R)⁰
x y : R
hy : y ∈ R⁰
hz : mk' (FractionRing R) x ⟨y, hy⟩ ≠ 0
h : spanSingleton R⁰ (mk' (FractionRing R) x ⟨y, hy⟩) * ↑↑I = ↑↑J
hx : x = 0
⊢ mk' (FractionRing R) x ⟨y, hy⟩ = 0

Proof state:
case refine_1.intro.intro
R : Type u_1
inst✝² : CommRing R
inst✝¹ : IsDomain R
inst✝ : IsDedekindDomain R
I J : ↥(Ideal R)⁰
z : FractionRing R
hz : z ≠ 0
h : spanSingleton R⁰ z * ↑↑I = ↑↑J
⊢ ∃ x y, ∃ (_ : x ≠ 0) (_ : y ≠ 0), Ideal.span {x} * ↑I = Ideal.span {y} * ↑J

Tactic:
obtain ⟨x, ⟨y, hy⟩, rfl⟩ := IsLocalization.mk'_surjective R⁰ z

Result:
case refine_1.intro.intro.intro.intro.mk
R : Type u_1
inst✝² : CommRing R
inst✝¹ : IsDomain R
inst✝ : IsDedekindDomain R
I J : ↥(Ideal R)⁰
x y : R
hy : y ∈ R⁰
hz : mk' (FractionRing R) x ⟨y, hy⟩ ≠ 0
h : spanSingleton R⁰ (mk' (FractionRing R) x ⟨y, hy⟩) * ↑↑I = ↑↑J
⊢ ∃ x y, ∃ (_ : x ≠ 0) (_ : y ≠ 0), Ideal.span {x} * ↑I = Ideal.span {y} * ↑J

Proof state:
R : Type u_1
inst✝² : CommRing R
inst✝¹ : IsDomain R
inst✝ : IsDedekindDomain R
I J : ↥(Ideal R)⁰
⊢ mk0 I = mk0 J ↔ ∃ x y, ∃ (_ : x ≠ 0) (_ : y ≠ 0), Ideal.span {x} * ↑I = Ideal.span {y} * ↑J

Tactic:
refine (ClassGroup.mk0_eq_mk0_iff_exists_fraction_ring (FractionRing R)).trans ⟨?_, ?_⟩

Result:
case refine_1
R : Type u_1
inst✝² : CommRing R
inst✝¹ : IsDomain R
inst✝ : IsDedekindDomain R
I J : ↥(Ideal R)⁰
⊢ (∃ x, ∃ (_ : x ≠ 0), spanSingleton R⁰ x * ↑↑I = ↑↑J) →
    ∃ x y, ∃ (_ : x ≠ 0) (_ : y ≠ 0), Ideal.span {x} * ↑I = Ideal.span {y} * ↑J

case refine_2
R : Type u_1
inst✝² : CommRing R
inst✝¹ : IsDomain R
inst✝ : IsDedekindDomain R
I J : ↥(Ideal R)⁰
⊢ (∃ x y, ∃ (_ : x ≠ 0) (_ : y ≠ 0), Ideal.span {x} * ↑I = Ideal.span {y} * ↑J) →
    ∃ x, ∃ (_ : x ≠ 0), spanSingleton R⁰ x * ↑↑I = ↑↑J

Proof state:
case refine_2.intro.intro.intro.intro.refine_1
R : Type u_1
inst✝² : CommRing R
inst✝¹ : IsDomain R
inst✝ : IsDedekindDomain R
I J : ↥(Ideal R)⁰
x y : R
hy : y ≠ 0
h : Ideal.span {x} * ↑I = Ideal.span {y} * ↑J
hy' : y ∈ R⁰
hx : mk' (FractionRing R) x ⟨y, hy'⟩ = 0
⊢ x = 0

Tactic:
rwa [mk'_eq_iff_eq_mul, zero_mul, ← (algebraMap R (FractionRing R)).map_zero,
  (IsFractionRing.injective R (FractionRing R)).eq_iff] at hx

Result:
no goals

Proof state:
case refine_2
R : Type u_1
inst✝² : CommRing R
inst✝¹ : IsDomain R
inst✝ : IsDedekindDomain R
I J : ↥(Ideal R)⁰
⊢ (∃ x y, ∃ (_ : x ≠ 0) (_ : y ≠ 0), Ideal.span {x} * ↑I = Ideal.span {y} * ↑J) →
    ∃ x, ∃ (_ : x ≠ 0), spanSingleton R⁰ x * ↑↑I = ↑↑J

Tactic:
rintro ⟨x, y, hx, hy, h⟩

Result:
case refine_2.intro.intro.intro.intro
R : Type u_1
inst✝² : CommRing R
inst✝¹ : IsDomain R
inst✝ : IsDedekindDomain R
I J : ↥(Ideal R)⁰
x y : R
hx : x ≠ 0
hy : y ≠ 0
h : Ideal.span {x} * ↑I = Ideal.span {y} * ↑J
⊢ ∃ x, ∃ (_ : x ≠ 0), spanSingleton R⁰ x * ↑↑I = ↑↑J

Proof state:
case refine_1
R : Type u_1
inst✝² : CommRing R
inst✝¹ : IsDomain R
inst✝ : IsDedekindDomain R
I J : ↥(Ideal R)⁰
⊢ (∃ x, ∃ (_ : x ≠ 0), spanSingleton R⁰ x * ↑↑I = ↑↑J) →
    ∃ x y, ∃ (_ : x ≠ 0) (_ : y ≠ 0), Ideal.span {x} * ↑I = Ideal.span {y} * ↑J

Tactic:
rintro ⟨z, hz, h⟩

Result:
case refine_1.intro.intro
R : Type u_1
inst✝² : CommRing R
inst✝¹ : IsDomain R
inst✝ : IsDedekindDomain R
I J : ↥(Ideal R)⁰
z : FractionRing R
hz : z ≠ 0
h : spanSingleton R⁰ z * ↑↑I = ↑↑J
⊢ ∃ x y, ∃ (_ : x ≠ 0) (_ : y ≠ 0), Ideal.span {x} * ↑I = Ideal.span {y} * ↑J

Proof state:
case refine_2.intro.intro.intro.intro.refine_1
R : Type u_1
inst✝² : CommRing R
inst✝¹ : IsDomain R
inst✝ : IsDedekindDomain R
I J : ↥(Ideal R)⁰
x y : R
hx : x ≠ 0
hy : y ≠ 0
h : Ideal.span {x} * ↑I = Ideal.span {y} * ↑J
hy' : y ∈ R⁰
⊢ mk' (FractionRing R) x ⟨y, hy'⟩ ≠ 0

Tactic:
contrapose! hx

Result:
case refine_2.intro.intro.intro.intro.refine_1
R : Type u_1
inst✝² : CommRing R
inst✝¹ : IsDomain R
inst✝ : IsDedekindDomain R
I J : ↥(Ideal R)⁰
x y : R
hy : y ≠ 0
h : Ideal.span {x} * ↑I = Ideal.span {y} * ↑J
hy' : y ∈ R⁰
hx : mk' (FractionRing R) x ⟨y, hy'⟩ = 0
⊢ x = 0

Proof state:
case refine_1.intro.intro.intro.intro.mk.refine_1
R : Type u_1
inst✝² : CommRing R
inst✝¹ : IsDomain R
inst✝ : IsDedekindDomain R
I J : ↥(Ideal R)⁰
x y : R
hy : y ∈ R⁰
hz : mk' (FractionRing R) x ⟨y, hy⟩ ≠ 0
h : spanSingleton R⁰ (mk' (FractionRing R) x ⟨y, hy⟩) * ↑↑I = ↑↑J
hx : x = 0
⊢ mk' (FractionRing R) x ⟨y, hy⟩ = 0

Tactic:
rw [hx, IsFractionRing.mk'_eq_div, _root_.map_zero, zero_div]

Result:
no goals