-- Mathlib/RingTheory/Ideal/Norm/RelNorm.lean
theorem spanNorm_mul (I J : Ideal S) : spanNorm R (I * J) = spanNorm R I * spanNorm R J

Proof state:
case he.h.a
R : Type u_1
inst✝¹² : CommRing R
inst✝¹¹ : IsDomain R
S : Type u_3
inst✝¹⁰ : CommRing S
inst✝⁹ : IsDomain S
inst✝⁸ : IsIntegrallyClosed R
inst✝⁷ : IsIntegrallyClosed S
inst✝⁶ : Algebra R S
inst✝⁵ : Module.Finite R S
inst✝⁴ : NoZeroSMulDivisors R S
inst✝³ : Algebra.IsSeparable (FractionRing R) (FractionRing S)
inst✝² : IsDedekindDomain R
inst✝¹ : IsDedekindDomain S
I J : Ideal S
inst✝ : Nontrivial R
h✝ : Nontrivial S
P : Ideal R
hP : P.IsMaximal
hP0 : ¬P = ⊥
P' : Submonoid S := Algebra.algebraMapSubmonoid S P.primeCompl
Rₚ : Type u_1 := Localization.AtPrime P
Sₚ : Type u_3 := Localization P'
x✝¹ : Algebra Rₚ Sₚ := localizationAlgebra P.primeCompl S
this✝⁶ : IsScalarTower R Rₚ Sₚ
h : P' ≤ S⁰
this✝⁵ : IsDomain Sₚ
this✝⁴ : IsDedekindDomain Sₚ
this✝³ : IsPrincipalIdealRing Sₚ
this✝² : NoZeroSMulDivisors Rₚ Sₚ
this✝¹ : Module.Finite Rₚ Sₚ
L : Type u_3 := FractionRing S
g : Sₚ →+* L := IsLocalization.map L (RingHom.id S) h
algInst✝ : Algebra Sₚ L := g.toAlgebra
this✝ : IsScalarTower S Sₚ (FractionRing S)
this : IsFractionRing Sₚ (FractionRing S)
x✝ : R
⊢ (algebraMap (FractionRing Rₚ) (FractionRing Sₚ)) ((algebraMap Rₚ (FractionRing Rₚ)) ((algebraMap R Rₚ) x✝)) =
    (algebraMap Sₚ (FractionRing Sₚ)) ((algebraMap S Sₚ) ((algebraMap R S) x✝))

Tactic:
simp only [← IsScalarTower.algebraMap_apply]

Result:
case he.h.a
R : Type u_1
inst✝¹² : CommRing R
inst✝¹¹ : IsDomain R
S : Type u_3
inst✝¹⁰ : CommRing S
inst✝⁹ : IsDomain S
inst✝⁸ : IsIntegrallyClosed R
inst✝⁷ : IsIntegrallyClosed S
inst✝⁶ : Algebra R S
inst✝⁵ : Module.Finite R S
inst✝⁴ : NoZeroSMulDivisors R S
inst✝³ : Algebra.IsSeparable (FractionRing R) (FractionRing S)
inst✝² : IsDedekindDomain R
inst✝¹ : IsDedekindDomain S
I J : Ideal S
inst✝ : Nontrivial R
h✝ : Nontrivial S
P : Ideal R
hP : P.IsMaximal
hP0 : ¬P = ⊥
P' : Submonoid S := Algebra.algebraMapSubmonoid S P.primeCompl
Rₚ : Type u_1 := Localization.AtPrime P
Sₚ : Type u_3 := Localization P'
x✝¹ : Algebra Rₚ Sₚ := localizationAlgebra P.primeCompl S
this✝⁶ : IsScalarTower R Rₚ Sₚ
h : P' ≤ S⁰
this✝⁵ : IsDomain Sₚ
this✝⁴ : IsDedekindDomain Sₚ
this✝³ : IsPrincipalIdealRing Sₚ
this✝² : NoZeroSMulDivisors Rₚ Sₚ
this✝¹ : Module.Finite Rₚ Sₚ
L : Type u_3 := FractionRing S
g : Sₚ →+* L := IsLocalization.map L (RingHom.id S) h
algInst✝ : Algebra Sₚ L := g.toAlgebra
this✝ : IsScalarTower S Sₚ (FractionRing S)
this : IsFractionRing Sₚ (FractionRing S)
x✝ : R
⊢ (algebraMap (FractionRing Rₚ) (FractionRing Sₚ)) ((algebraMap R (FractionRing Rₚ)) x✝) =
    (algebraMap R (FractionRing Sₚ)) x✝

Proof state:
case neg
R : Type u_1
inst✝¹² : CommRing R
inst✝¹¹ : IsDomain R
S : Type u_3
inst✝¹⁰ : CommRing S
inst✝⁹ : IsDomain S
inst✝⁸ : IsIntegrallyClosed R
inst✝⁷ : IsIntegrallyClosed S
inst✝⁶ : Algebra R S
inst✝⁵ : Module.Finite R S
inst✝⁴ : NoZeroSMulDivisors R S
inst✝³ : Algebra.IsSeparable (FractionRing R) (FractionRing S)
inst✝² : IsDedekindDomain R
inst✝¹ : IsDedekindDomain S
I J : Ideal S
inst✝ : Nontrivial R
h✝ : Nontrivial S
P : Ideal R
hP : P.IsMaximal
hP0 : ¬P = ⊥
P' : Submonoid S := Algebra.algebraMapSubmonoid S P.primeCompl
Rₚ : Type u_1 := Localization.AtPrime P
Sₚ : Type u_3 := Localization P'
x✝ : Algebra Rₚ Sₚ := localizationAlgebra P.primeCompl S
this✝⁵ : IsScalarTower R Rₚ Sₚ
h : P' ≤ S⁰
this✝⁴ : IsDomain Sₚ
this✝³ : IsDedekindDomain Sₚ
this✝² : IsPrincipalIdealRing Sₚ
this✝¹ : NoZeroSMulDivisors Rₚ Sₚ
this✝ : Module.Finite Rₚ Sₚ
L : Type u_3 := FractionRing S
g : Sₚ →+* L := IsLocalization.map L (RingHom.id S) h
algInst✝ : Algebra Sₚ L := g.toAlgebra
this : IsScalarTower S Sₚ (FractionRing S)
⊢ map (algebraMap R (Localization.AtPrime P)) (spanNorm R (I * J)) =
    map (algebraMap R (Localization.AtPrime P)) (spanNorm R I * spanNorm R J)

Tactic:
have := IsFractionRing.isFractionRing_of_isDomain_of_isLocalization P' Sₚ (FractionRing S)

Result:
case neg
R : Type u_1
inst✝¹² : CommRing R
inst✝¹¹ : IsDomain R
S : Type u_3
inst✝¹⁰ : CommRing S
inst✝⁹ : IsDomain S
inst✝⁸ : IsIntegrallyClosed R
inst✝⁷ : IsIntegrallyClosed S
inst✝⁶ : Algebra R S
inst✝⁵ : Module.Finite R S
inst✝⁴ : NoZeroSMulDivisors R S
inst✝³ : Algebra.IsSeparable (FractionRing R) (FractionRing S)
inst✝² : IsDedekindDomain R
inst✝¹ : IsDedekindDomain S
I J : Ideal S
inst✝ : Nontrivial R
h✝ : Nontrivial S
P : Ideal R
hP : P.IsMaximal
hP0 : ¬P = ⊥
P' : Submonoid S := Algebra.algebraMapSubmonoid S P.primeCompl
Rₚ : Type u_1 := Localization.AtPrime P
Sₚ : Type u_3 := Localization P'
x✝ : Algebra Rₚ Sₚ := localizationAlgebra P.primeCompl S
this✝⁶ : IsScalarTower R Rₚ Sₚ
h : P' ≤ S⁰
this✝⁵ : IsDomain Sₚ
this✝⁴ : IsDedekindDomain Sₚ
this✝³ : IsPrincipalIdealRing Sₚ
this✝² : NoZeroSMulDivisors Rₚ Sₚ
this✝¹ : Module.Finite Rₚ Sₚ
L : Type u_3 := FractionRing S
g : Sₚ →+* L := IsLocalization.map L (RingHom.id S) h
algInst✝ : Algebra Sₚ L := g.toAlgebra
this✝ : IsScalarTower S Sₚ (FractionRing S)
this : IsFractionRing Sₚ (FractionRing S)
⊢ map (algebraMap R (Localization.AtPrime P)) (spanNorm R (I * J)) =
    map (algebraMap R (Localization.AtPrime P)) (spanNorm R I * spanNorm R J)

Proof state:
case pos
R : Type u_1
inst✝¹² : CommRing R
inst✝¹¹ : IsDomain R
S : Type u_3
inst✝¹⁰ : CommRing S
inst✝⁹ : IsDomain S
inst✝⁸ : IsIntegrallyClosed R
inst✝⁷ : IsIntegrallyClosed S
inst✝⁶ : Algebra R S
inst✝⁵ : Module.Finite R S
inst✝⁴ : NoZeroSMulDivisors R S
inst✝³ : Algebra.IsSeparable (FractionRing R) (FractionRing S)
inst✝² : IsDedekindDomain R
inst✝¹ : IsDedekindDomain S
I J : Ideal S
inst✝ : Nontrivial R
h✝ : Nontrivial S
hP : ⊥.IsMaximal
⊢ map (algebraMap R (Localization.AtPrime ⊥)) (spanNorm R (I * J)) =
    map (algebraMap R (Localization.AtPrime ⊥)) (spanNorm R I * spanNorm R J)

Tactic:
rw [spanNorm_mul_of_bot_or_top]

Result:
case pos.eq_bot_or_top
R : Type u_1
inst✝¹² : CommRing R
inst✝¹¹ : IsDomain R
S : Type u_3
inst✝¹⁰ : CommRing S
inst✝⁹ : IsDomain S
inst✝⁸ : IsIntegrallyClosed R
inst✝⁷ : IsIntegrallyClosed S
inst✝⁶ : Algebra R S
inst✝⁵ : Module.Finite R S
inst✝⁴ : NoZeroSMulDivisors R S
inst✝³ : Algebra.IsSeparable (FractionRing R) (FractionRing S)
inst✝² : IsDedekindDomain R
inst✝¹ : IsDedekindDomain S
I J : Ideal S
inst✝ : Nontrivial R
h✝ : Nontrivial S
hP : ⊥.IsMaximal
⊢ ∀ (I : Ideal R), I = ⊥ ∨ I = ⊤