Theorem: Submodule.prod_span
File: Mathlib/Algebra/Algebra/Operations.lean

tactic: letI := Classical.decEq ι
state_before: ι✝ : Sort uι
R : Type u
inst✝² : CommSemiring R
A : Type v
inst✝¹ : CommSemiring A
inst✝ : Algebra R A
M✝ N : Submodule R A
m n : A
ι : Type u_1
s : Finset ι
M : ι → Set A
⊢ ∏ i ∈ s, span R (M i) = span R (∏ i ∈ s, M i)
state_after: ι✝ : Sort uι
R : Type u
inst✝² : CommSemiring R
A : Type v
inst✝¹ : CommSemiring A
inst✝ : Algebra R A
M✝ N : Submodule R A
m n : A
ι : Type u_1
s : Finset ι
M : ι → Set A
this : DecidableEq ι := Classical.decEq ι
⊢ ∏ i ∈ s, span R (M i) = span R (∏ i ∈ s, M i)

tactic: refine Finset.induction_on s ?_ ?_
state_before: ι✝ : Sort uι
R : Type u
inst✝² : CommSemiring R
A : Type v
inst✝¹ : CommSemiring A
inst✝ : Algebra R A
M✝ N : Submodule R A
m n : A
ι : Type u_1
s : Finset ι
M : ι → Set A
this : DecidableEq ι := Classical.decEq ι
⊢ ∏ i ∈ s, span R (M i) = span R (∏ i ∈ s, M i)
state_after: case refine_1
ι✝ : Sort uι
R : Type u
inst✝² : CommSemiring R
A : Type v
inst✝¹ : CommSemiring A
inst✝ : Algebra R A
M✝ N : Submodule R A
m n : A
ι : Type u_1
s : Finset ι
M : ι → Set A
this : DecidableEq ι := Classical.decEq ι
⊢ ∏ i ∈ ∅, span R (M i) = span R (∏ i ∈ ∅, M i)

case refine_2
ι✝ : Sort uι
R : Type u
inst✝² : CommSemiring R
A : Type v
inst✝¹ : CommSemiring A
inst✝ : Algebra R A
M✝ N : Submodule R A
m n : A
ι : Type u_1
s : Finset ι
M : ι → Set A
this : DecidableEq ι := Classical.decEq ι
⊢ ∀ ⦃a : ι⦄ {s : Finset ι},
    a ∉ s →
      ∏ i ∈ s, span R (M i) = span R (∏ i ∈ s, M i) → ∏ i ∈ insert a s, span R (M i) = span R (∏ i ∈ insert a s, M i)

tactic: simp [one_eq_span, Set.singleton_one]
state_before: case refine_1
ι✝ : Sort uι
R : Type u
inst✝² : CommSemiring R
A : Type v
inst✝¹ : CommSemiring A
inst✝ : Algebra R A
M✝ N : Submodule R A
m n : A
ι : Type u_1
s : Finset ι
M : ι → Set A
this : DecidableEq ι := Classical.decEq ι
⊢ ∏ i ∈ ∅, span R (M i) = span R (∏ i ∈ ∅, M i)
state_after: no goals

tactic: intro _ _ H ih
state_before: case refine_2
ι✝ : Sort uι
R : Type u
inst✝² : CommSemiring R
A : Type v
inst✝¹ : CommSemiring A
inst✝ : Algebra R A
M✝ N : Submodule R A
m n : A
ι : Type u_1
s : Finset ι
M : ι → Set A
this : DecidableEq ι := Classical.decEq ι
⊢ ∀ ⦃a : ι⦄ {s : Finset ι},
    a ∉ s →
      ∏ i ∈ s, span R (M i) = span R (∏ i ∈ s, M i) → ∏ i ∈ insert a s, span R (M i) = span R (∏ i ∈ insert a s, M i)
state_after: case refine_2
ι✝ : Sort uι
R : Type u
inst✝² : CommSemiring R
A : Type v
inst✝¹ : CommSemiring A
inst✝ : Algebra R A
M✝ N : Submodule R A
m n : A
ι : Type u_1
s : Finset ι
M : ι → Set A
this : DecidableEq ι := Classical.decEq ι
a✝ : ι
s✝ : Finset ι
H : a✝ ∉ s✝
ih : ∏ i ∈ s✝, span R (M i) = span R (∏ i ∈ s✝, M i)
⊢ ∏ i ∈ insert a✝ s✝, span R (M i) = span R (∏ i ∈ insert a✝ s✝, M i)

tactic: rw [Finset.prod_insert H, Finset.prod_insert H, ih, span_mul_span]
state_before: case refine_2
ι✝ : Sort uι
R : Type u
inst✝² : CommSemiring R
A : Type v
inst✝¹ : CommSemiring A
inst✝ : Algebra R A
M✝ N : Submodule R A
m n : A
ι : Type u_1
s : Finset ι
M : ι → Set A
this : DecidableEq ι := Classical.decEq ι
a✝ : ι
s✝ : Finset ι
H : a✝ ∉ s✝
ih : ∏ i ∈ s✝, span R (M i) = span R (∏ i ∈ s✝, M i)
⊢ ∏ i ∈ insert a✝ s✝, span R (M i) = span R (∏ i ∈ insert a✝ s✝, M i)
state_after: no goals