-- Mathlib/NumberTheory/KummerDedekind.lean
theorem prod_mem_ideal_map_of_mem_conductor {p : R} {z : S}
    (hp : p ∈ Ideal.comap (algebraMap R S) (conductor R x)) (hz' : z ∈ I.map (algebraMap R S)) :
    algebraMap R S p * z ∈ algebraMap R<x> S '' ↑(I.map (algebraMap R R<x>))

Proof state:
case intro.intro.refine_2
R : Type u_1
S : Type u_2
inst✝² : CommRing R
inst✝¹ : CommRing S
inst✝ : Algebra R S
x : S
I : Ideal R
p : R
z : S
hp : p ∈ comap (algebraMap R S) (conductor R x)
l : R →₀ S
H : l ∈ Finsupp.supported S S ↑I
H' : (l.sum fun i a => a • (algebraMap R S) i) = z
lem :
  ∀ {a : R},
    a ∈ I →
      l a • (algebraMap R S) a * (algebraMap R S) p ∈
        ⇑(algebraMap (↥(adjoin R {x})) S) '' ↑(Ideal.map (algebraMap R ↥(adjoin R {x})) I)
⊢ (fun u => u ∈ ⇑(algebraMap (↥(adjoin R {x})) S) '' ↑(Ideal.map (algebraMap R ↥(adjoin R {x})) I)) 0

Tactic:
exact ⟨0, SetLike.mem_coe.mpr <| Ideal.zero_mem _, RingHom.map_zero _⟩

Result:
no goals

Proof state:
case intro.intro.refine_1
R : Type u_1
S : Type u_2
inst✝² : CommRing R
inst✝¹ : CommRing S
inst✝ : Algebra R S
x : S
I : Ideal R
p : R
z : S
hp : p ∈ comap (algebraMap R S) (conductor R x)
l : R →₀ S
H : l ∈ Finsupp.supported S S ↑I
H' : (l.sum fun i a => a • (algebraMap R S) i) = z
lem :
  ∀ {a : R},
    a ∈ I →
      l a • (algebraMap R S) a * (algebraMap R S) p ∈
        ⇑(algebraMap (↥(adjoin R {x})) S) '' ↑(Ideal.map (algebraMap R ↥(adjoin R {x})) I)
a b : S
⊢ (fun u => u ∈ ⇑(algebraMap (↥(adjoin R {x})) S) '' ↑(Ideal.map (algebraMap R ↥(adjoin R {x})) I)) a →
    (fun u => u ∈ ⇑(algebraMap (↥(adjoin R {x})) S) '' ↑(Ideal.map (algebraMap R ↥(adjoin R {x})) I)) b →
      (fun u => u ∈ ⇑(algebraMap (↥(adjoin R {x})) S) '' ↑(Ideal.map (algebraMap R ↥(adjoin R {x})) I)) (a + b)

Tactic:
rintro ⟨z, hz, rfl⟩ ⟨y, hy, rfl⟩

Result:
case intro.intro.refine_1.intro.intro.intro.intro
R : Type u_1
S : Type u_2
inst✝² : CommRing R
inst✝¹ : CommRing S
inst✝ : Algebra R S
x : S
I : Ideal R
p : R
z✝ : S
hp : p ∈ comap (algebraMap R S) (conductor R x)
l : R →₀ S
H : l ∈ Finsupp.supported S S ↑I
H' : (l.sum fun i a => a • (algebraMap R S) i) = z✝
lem :
  ∀ {a : R},
    a ∈ I →
      l a • (algebraMap R S) a * (algebraMap R S) p ∈
        ⇑(algebraMap (↥(adjoin R {x})) S) '' ↑(Ideal.map (algebraMap R ↥(adjoin R {x})) I)
z : ↥(adjoin R {x})
hz : z ∈ ↑(Ideal.map (algebraMap R ↥(adjoin R {x})) I)
y : ↥(adjoin R {x})
hy : y ∈ ↑(Ideal.map (algebraMap R ↥(adjoin R {x})) I)
⊢ (algebraMap (↥(adjoin R {x})) S) z + (algebraMap (↥(adjoin R {x})) S) y ∈
    ⇑(algebraMap (↥(adjoin R {x})) S) '' ↑(Ideal.map (algebraMap R ↥(adjoin R {x})) I)

Proof state:
case intro.intro
R : Type u_1
S : Type u_2
inst✝² : CommRing R
inst✝¹ : CommRing S
inst✝ : Algebra R S
x : S
I : Ideal R
p : R
z : S
hp : p ∈ comap (algebraMap R S) (conductor R x)
l : R →₀ S
H : l ∈ Finsupp.supported S S ↑I
H' : (l.sum fun i a => a • (algebraMap R S) i) = z
⊢ (algebraMap R S) p * z ∈ ⇑(algebraMap (↥(adjoin R {x})) S) '' ↑(Ideal.map (algebraMap R ↥(adjoin R {x})) I)

Tactic:
rw [← H', mul_comm, Finsupp.sum_mul]

Result:
case intro.intro
R : Type u_1
S : Type u_2
inst✝² : CommRing R
inst✝¹ : CommRing S
inst✝ : Algebra R S
x : S
I : Ideal R
p : R
z : S
hp : p ∈ comap (algebraMap R S) (conductor R x)
l : R →₀ S
H : l ∈ Finsupp.supported S S ↑I
H' : (l.sum fun i a => a • (algebraMap R S) i) = z
⊢ (l.sum fun a c => c • (algebraMap R S) a * (algebraMap R S) p) ∈
    ⇑(algebraMap (↥(adjoin R {x})) S) '' ↑(Ideal.map (algebraMap R ↥(adjoin R {x})) I)

Proof state:
case intro.intro.refine_1.intro.intro.intro.intro
R : Type u_1
S : Type u_2
inst✝² : CommRing R
inst✝¹ : CommRing S
inst✝ : Algebra R S
x : S
I : Ideal R
p : R
z✝ : S
hp : p ∈ comap (algebraMap R S) (conductor R x)
l : R →₀ S
H : l ∈ Finsupp.supported S S ↑I
H' : (l.sum fun i a => a • (algebraMap R S) i) = z✝
lem :
  ∀ {a : R},
    a ∈ I →
      l a • (algebraMap R S) a * (algebraMap R S) p ∈
        ⇑(algebraMap (↥(adjoin R {x})) S) '' ↑(Ideal.map (algebraMap R ↥(adjoin R {x})) I)
z : ↥(adjoin R {x})
hz : z ∈ ↑(Ideal.map (algebraMap R ↥(adjoin R {x})) I)
y : ↥(adjoin R {x})
hy : y ∈ ↑(Ideal.map (algebraMap R ↥(adjoin R {x})) I)
⊢ (algebraMap (↥(adjoin R {x})) S) z + (algebraMap (↥(adjoin R {x})) S) y ∈
    ⇑(algebraMap (↥(adjoin R {x})) S) '' ↑(Ideal.map (algebraMap R ↥(adjoin R {x})) I)

Tactic:
rw [← RingHom.map_add]

Result:
case intro.intro.refine_1.intro.intro.intro.intro
R : Type u_1
S : Type u_2
inst✝² : CommRing R
inst✝¹ : CommRing S
inst✝ : Algebra R S
x : S
I : Ideal R
p : R
z✝ : S
hp : p ∈ comap (algebraMap R S) (conductor R x)
l : R →₀ S
H : l ∈ Finsupp.supported S S ↑I
H' : (l.sum fun i a => a • (algebraMap R S) i) = z✝
lem :
  ∀ {a : R},
    a ∈ I →
      l a • (algebraMap R S) a * (algebraMap R S) p ∈
        ⇑(algebraMap (↥(adjoin R {x})) S) '' ↑(Ideal.map (algebraMap R ↥(adjoin R {x})) I)
z : ↥(adjoin R {x})
hz : z ∈ ↑(Ideal.map (algebraMap R ↥(adjoin R {x})) I)
y : ↥(adjoin R {x})
hy : y ∈ ↑(Ideal.map (algebraMap R ↥(adjoin R {x})) I)
⊢ (algebraMap (↥(adjoin R {x})) S) (z + y) ∈
    ⇑(algebraMap (↥(adjoin R {x})) S) '' ↑(Ideal.map (algebraMap R ↥(adjoin R {x})) I)

Proof state:
case refine_1
R : Type u_1
S : Type u_2
inst✝² : CommRing R
inst✝¹ : CommRing S
inst✝ : Algebra R S
x : S
I : Ideal R
p : R
z : S
hp : p ∈ comap (algebraMap R S) (conductor R x)
l : R →₀ S
H : l ∈ Finsupp.supported S S ↑I
H' : (l.sum fun i a => a • (algebraMap R S) i) = z
a : R
ha : a ∈ I
⊢ ⟨l a * (algebraMap R S) p, ⋯⟩ * (algebraMap R ↥(adjoin R {x})) a ∈ ↑(Ideal.map (algebraMap R ↥(adjoin R {x})) I)

Tactic:
apply Ideal.mul_mem_left (I.map (algebraMap R R<x>)) _ (Ideal.mem_map_of_mem _ ha)

Result:
no goals

Proof state:
R : Type u_1
S : Type u_2
inst✝² : CommRing R
inst✝¹ : CommRing S
inst✝ : Algebra R S
x : S
I : Ideal R
p : R
z : S
hp : p ∈ comap (algebraMap R S) (conductor R x)
hz' : ∃ l ∈ Finsupp.supported S S ↑I, (Finsupp.linearCombination S ⇑(algebraMap R S)) l = z
⊢ (algebraMap R S) p * z ∈ ⇑(algebraMap (↥(adjoin R {x})) S) '' ↑(Ideal.map (algebraMap R ↥(adjoin R {x})) I)

Tactic:
obtain ⟨l, H, H'⟩ := hz'

Result:
case intro.intro
R : Type u_1
S : Type u_2
inst✝² : CommRing R
inst✝¹ : CommRing S
inst✝ : Algebra R S
x : S
I : Ideal R
p : R
z : S
hp : p ∈ comap (algebraMap R S) (conductor R x)
l : R →₀ S
H : l ∈ Finsupp.supported S S ↑I
H' : (Finsupp.linearCombination S ⇑(algebraMap R S)) l = z
⊢ (algebraMap R S) p * z ∈ ⇑(algebraMap (↥(adjoin R {x})) S) '' ↑(Ideal.map (algebraMap R ↥(adjoin R {x})) I)

Proof state:
case intro.intro.refine_3
R : Type u_1
S : Type u_2
inst✝² : CommRing R
inst✝¹ : CommRing S
inst✝ : Algebra R S
x : S
I : Ideal R
p : R
z : S
hp : p ∈ comap (algebraMap R S) (conductor R x)
l : R →₀ S
H : l ∈ Finsupp.supported S S ↑I
H' : (l.sum fun i a => a • (algebraMap R S) i) = z
lem :
  ∀ {a : R},
    a ∈ I →
      l a • (algebraMap R S) a * (algebraMap R S) p ∈
        ⇑(algebraMap (↥(adjoin R {x})) S) '' ↑(Ideal.map (algebraMap R ↥(adjoin R {x})) I)
⊢ ∀ x_1 ∈ l.support,
    (fun u => u ∈ ⇑(algebraMap (↥(adjoin R {x})) S) '' ↑(Ideal.map (algebraMap R ↥(adjoin R {x})) I))
      ((fun a c => c • (algebraMap R S) a * (algebraMap R S) p) x_1 (l x_1))

Tactic:
intro y hy

Result:
case intro.intro.refine_3
R : Type u_1
S : Type u_2
inst✝² : CommRing R
inst✝¹ : CommRing S
inst✝ : Algebra R S
x : S
I : Ideal R
p : R
z : S
hp : p ∈ comap (algebraMap R S) (conductor R x)
l : R →₀ S
H : l ∈ Finsupp.supported S S ↑I
H' : (l.sum fun i a => a • (algebraMap R S) i) = z
lem :
  ∀ {a : R},
    a ∈ I →
      l a • (algebraMap R S) a * (algebraMap R S) p ∈
        ⇑(algebraMap (↥(adjoin R {x})) S) '' ↑(Ideal.map (algebraMap R ↥(adjoin R {x})) I)
y : R
hy : y ∈ l.support
⊢ (fun a c => c • (algebraMap R S) a * (algebraMap R S) p) y (l y) ∈
    ⇑(algebraMap (↥(adjoin R {x})) S) '' ↑(Ideal.map (algebraMap R ↥(adjoin R {x})) I)