Theorem: isCoprime_Inf (LeanCourse/MIL/C08_Groups_and_Rings/solutions/Solutions_S02_Rings.lean)

State before:
ι : Type u_1
R : Type u_2
inst✝ : CommRing R
I : Ideal R
J : ι → Ideal R
s : Finset ι
hf : ∀ j ∈ s, IsCoprime I (J j)
⊢ IsCoprime I (⨅ j ∈ s, J j)
Tactic:
classical
simp_rw [isCoprime_iff_add] at *
induction s using Finset.induction with
| empty =>
    simp
| @insert i s _ hs =>
    rw [Finset.iInf_insert, inf_comm, one_eq_top, eq_top_iff, ← one_eq_top]
    set K := ⨅ j ∈ s, J j
    calc
      1 = I + K            := (hs fun j hj ↦ hf j (Finset.mem_insert_of_mem hj)).symm
      _ = I + K*(I + J i)  := by rw [hf i (Finset.mem_insert_self i s), mul_one]
      _ = (1+K)*I + K*J i  := by ring
      _ ≤ I + K ⊓ J i      := by gcongr ; apply mul_le_left ; apply mul_le_inf
State after:
no goals

State before:
ι : Type u_1
R : Type u_2
inst✝ : CommRing R
I : Ideal R
J : ι → Ideal R
s : Finset ι
hf : ∀ j ∈ s, IsCoprime I (J j)
⊢ IsCoprime I (⨅ j ∈ s, J j)
Tactic:
simp_rw [isCoprime_iff_add] at *
State after:
ι : Type u_1
R : Type u_2
inst✝ : CommRing R
I : Ideal R
J : ι → Ideal R
s : Finset ι
hf : ∀ j ∈ s, I + J j = 1
⊢ I + ⨅ j ∈ s, J j = 1

State before:
ι : Type u_1
R : Type u_2
inst✝ : CommRing R
I : Ideal R
J : ι → Ideal R
s : Finset ι
hf : ∀ j ∈ s, I + J j = 1
⊢ I + ⨅ j ∈ s, J j = 1
Tactic:
induction s using Finset.induction with
| empty =>
    simp
| @insert i s _ hs =>
    rw [Finset.iInf_insert, inf_comm, one_eq_top, eq_top_iff, ← one_eq_top]
    set K := ⨅ j ∈ s, J j
    calc
      1 = I + K            := (hs fun j hj ↦ hf j (Finset.mem_insert_of_mem hj)).symm
      _ = I + K*(I + J i)  := by rw [hf i (Finset.mem_insert_self i s), mul_one]
      _ = (1+K)*I + K*J i  := by ring
      _ ≤ I + K ⊓ J i      := by gcongr ; apply mul_le_left ; apply mul_le_inf
State after:
no goals

State before:
case empty
ι : Type u_1
R : Type u_2
inst✝ : CommRing R
I : Ideal R
J : ι → Ideal R
hf : ∀ j ∈ ∅, I + J j = 1
⊢ I + ⨅ j ∈ ∅, J j = 1
Tactic:
simp
State after:
no goals

State before:
case insert
ι : Type u_1
R : Type u_2
inst✝ : CommRing R
I : Ideal R
J : ι → Ideal R
i : ι
s : Finset ι
a✝ : i ∉ s
hs : (∀ j ∈ s, I + J j = 1) → I + ⨅ j ∈ s, J j = 1
hf : ∀ j ∈ insert i s, I + J j = 1
⊢ I + ⨅ j ∈ insert i s, J j = 1
Tactic:
rw [Finset.iInf_insert, inf_comm, one_eq_top, eq_top_iff, ← one_eq_top]
State after:
case insert
ι : Type u_1
R : Type u_2
inst✝ : CommRing R
I : Ideal R
J : ι → Ideal R
i : ι
s : Finset ι
a✝ : i ∉ s
hs : (∀ j ∈ s, I + J j = 1) → I + ⨅ j ∈ s, J j = 1
hf : ∀ j ∈ insert i s, I + J j = 1
⊢ 1 ≤ I + (⨅ x ∈ s, J x) ⊓ J i

State before:
case insert
ι : Type u_1
R : Type u_2
inst✝ : CommRing R
I : Ideal R
J : ι → Ideal R
i : ι
s : Finset ι
a✝ : i ∉ s
hs : (∀ j ∈ s, I + J j = 1) → I + ⨅ j ∈ s, J j = 1
hf : ∀ j ∈ insert i s, I + J j = 1
⊢ 1 ≤ I + (⨅ x ∈ s, J x) ⊓ J i
Tactic:
set K := ⨅ j ∈ s, J j
State after:
case insert
ι : Type u_1
R : Type u_2
inst✝ : CommRing R
I : Ideal R
J : ι → Ideal R
i : ι
s : Finset ι
a✝ : i ∉ s
hf : ∀ j ∈ insert i s, I + J j = 1
K : Ideal R := ⨅ j ∈ s, J j
hs : (∀ j ∈ s, I + J j = 1) → I + K = 1
⊢ 1 ≤ I + K ⊓ J i

State before:
case insert
ι : Type u_1
R : Type u_2
inst✝ : CommRing R
I : Ideal R
J : ι → Ideal R
i : ι
s : Finset ι
a✝ : i ∉ s
hf : ∀ j ∈ insert i s, I + J j = 1
K : Ideal R := ⨅ j ∈ s, J j
hs : (∀ j ∈ s, I + J j = 1) → I + K = 1
⊢ 1 ≤ I + K ⊓ J i
Tactic:
calc
  1 = I + K            := (hs fun j hj ↦ hf j (Finset.mem_insert_of_mem hj)).symm
  _ = I + K*(I + J i)  := by rw [hf i (Finset.mem_insert_self i s), mul_one]
  _ = (1+K)*I + K*J i  := by ring
  _ ≤ I + K ⊓ J i      := by gcongr ; apply mul_le_left ; apply mul_le_inf
State after:
no goals

State before:
ι : Type u_1
R : Type u_2
inst✝ : CommRing R
I : Ideal R
J : ι → Ideal R
i : ι
s : Finset ι
a✝ : i ∉ s
hf : ∀ j ∈ insert i s, I + J j = 1
K : Ideal R := ⨅ j ∈ s, J j
hs : (∀ j ∈ s, I + J j = 1) → I + K = 1
⊢ I + K = I + K * (I + J i)
Tactic:
rw [hf i (Finset.mem_insert_self i s), mul_one]
State after:
no goals

State before:
ι : Type u_1
R : Type u_2
inst✝ : CommRing R
I : Ideal R
J : ι → Ideal R
i : ι
s : Finset ι
a✝ : i ∉ s
hf : ∀ j ∈ insert i s, I + J j = 1
K : Ideal R := ⨅ j ∈ s, J j
hs : (∀ j ∈ s, I + J j = 1) → I + K = 1
⊢ I + K * (I + J i) = (1 + K) * I + K * J i
Tactic:
ring
State after:
no goals

State before:
ι : Type u_1
R : Type u_2
inst✝ : CommRing R
I : Ideal R
J : ι → Ideal R
i : ι
s : Finset ι
a✝ : i ∉ s
hf : ∀ j ∈ insert i s, I + J j = 1
K : Ideal R := ⨅ j ∈ s, J j
hs : (∀ j ∈ s, I + J j = 1) → I + K = 1
⊢ (1 + K) * I + K * J i ≤ I + K ⊓ J i
Tactic:
gcongr
State after:
case h₁
ι : Type u_1
R : Type u_2
inst✝ : CommRing R
I : Ideal R
J : ι → Ideal R
i : ι
s : Finset ι
a✝ : i ∉ s
hf : ∀ j ∈ insert i s, I + J j = 1
K : Ideal R := ⨅ j ∈ s, J j
hs : (∀ j ∈ s, I + J j = 1) → I + K = 1
⊢ (1 + K) * I ≤ I

case h₂
ι : Type u_1
R : Type u_2
inst✝ : CommRing R
I : Ideal R
J : ι → Ideal R
i : ι
s : Finset ι
a✝ : i ∉ s
hf : ∀ j ∈ insert i s, I + J j = 1
K : Ideal R := ⨅ j ∈ s, J j
hs : (∀ j ∈ s, I + J j = 1) → I + K = 1
⊢ K * J i ≤ K ⊓ J i

State before:
case h₁
ι : Type u_1
R : Type u_2
inst✝ : CommRing R
I : Ideal R
J : ι → Ideal R
i : ι
s : Finset ι
a✝ : i ∉ s
hf : ∀ j ∈ insert i s, I + J j = 1
K : Ideal R := ⨅ j ∈ s, J j
hs : (∀ j ∈ s, I + J j = 1) → I + K = 1
⊢ (1 + K) * I ≤ I

case h₂
ι : Type u_1
R : Type u_2
inst✝ : CommRing R
I : Ideal R
J : ι → Ideal R
i : ι
s : Finset ι
a✝ : i ∉ s
hf : ∀ j ∈ insert i s, I + J j = 1
K : Ideal R := ⨅ j ∈ s, J j
hs : (∀ j ∈ s, I + J j = 1) → I + K = 1
⊢ K * J i ≤ K ⊓ J i
Tactic:
apply mul_le_left
State after:
case h₂
ι : Type u_1
R : Type u_2
inst✝ : CommRing R
I : Ideal R
J : ι → Ideal R
i : ι
s : Finset ι
a✝ : i ∉ s
hf : ∀ j ∈ insert i s, I + J j = 1
K : Ideal R := ⨅ j ∈ s, J j
hs : (∀ j ∈ s, I + J j = 1) → I + K = 1
⊢ K * J i ≤ K ⊓ J i

State before:
case h₂
ι : Type u_1
R : Type u_2
inst✝ : CommRing R
I : Ideal R
J : ι → Ideal R
i : ι
s : Finset ι
a✝ : i ∉ s
hf : ∀ j ∈ insert i s, I + J j = 1
K : Ideal R := ⨅ j ∈ s, J j
hs : (∀ j ∈ s, I + J j = 1) → I + K = 1
⊢ K * J i ≤ K ⊓ J i
Tactic:
apply mul_le_inf
State after:
no goals