Theorem: Polynomial.mem_span_C_coeff
File: Mathlib/Algebra/Polynomial/Induction.lean

Proof steps:
state_before: R : Type u
S : Type v
T : Type w
ι : Type x
k : Type y
A : Type z
a b : R
m n : ℕ
inst✝ : Semiring R
p q r f : R[X]
I : Ideal R[X]
⊢ f ∈ Ideal.span {g | ∃ i, g = C (f.coeff i)}
state_after: R : Type u
S : Type v
T : Type w
ι : Type x
k : Type y
A : Type z
a b : R
m n : ℕ
inst✝ : Semiring R
p✝ q r f : R[X]
I : Ideal R[X]
p : Ideal R[X] := Ideal.span {g | ∃ i, g = C (f.coeff i)}
⊢ f ∈ Ideal.span {g | ∃ i, g = C (f.coeff i)}
tactic: let p := Ideal.span { g : R[X] | ∃ i : ℕ, g = C (coeff f i) }
state_before: R : Type u
S : Type v
T : Type w
ι : Type x
k : Type y
A : Type z
a b : R
m n : ℕ
inst✝ : Semiring R
p✝ q r f : R[X]
I : Ideal R[X]
p : Ideal R[X] := Ideal.span {g | ∃ i, g = C (f.coeff i)}
⊢ f ∈ Ideal.span {g | ∃ i, g = C (f.coeff i)}
state_after: R : Type u
S : Type v
T : Type w
ι : Type x
k : Type y
A : Type z
a b : R
m n : ℕ
inst✝ : Semiring R
p✝ q r f : R[X]
I : Ideal R[X]
p : Ideal R[X] := Ideal.span {g | ∃ i, g = C (f.coeff i)}
⊢ (f.sum fun n a => C a * X ^ n) ∈ Ideal.span {g | ∃ i, g = C (f.coeff i)}
tactic: nth_rw 1 [(sum_C_mul_X_pow_eq f).symm]
state_before: R : Type u
S : Type v
T : Type w
ι : Type x
k : Type y
A : Type z
a b : R
m n : ℕ
inst✝ : Semiring R
p✝ q r f : R[X]
I : Ideal R[X]
p : Ideal R[X] := Ideal.span {g | ∃ i, g = C (f.coeff i)}
⊢ (f.sum fun n a => C a * X ^ n) ∈ Ideal.span {g | ∃ i, g = C (f.coeff i)}
state_after: R : Type u
S : Type v
T : Type w
ι : Type x
k : Type y
A : Type z
a b : R
m n✝ : ℕ
inst✝ : Semiring R
p✝ q r f : R[X]
I : Ideal R[X]
p : Ideal R[X] := Ideal.span {g | ∃ i, g = C (f.coeff i)}
n : ℕ
_hn : n ∈ f.support
⊢ (fun n a => C a * X ^ n) n (f.coeff n) ∈ Ideal.span {g | ∃ i, g = C (f.coeff i)}
tactic: refine Submodule.sum_mem _ fun n _hn => ?_
state_before: R : Type u
S : Type v
T : Type w
ι : Type x
k : Type y
A : Type z
a b : R
m n✝ : ℕ
inst✝ : Semiring R
p✝ q r f : R[X]
I : Ideal R[X]
p : Ideal R[X] := Ideal.span {g | ∃ i, g = C (f.coeff i)}
n : ℕ
_hn : n ∈ f.support
⊢ (fun n a => C a * X ^ n) n (f.coeff n) ∈ Ideal.span {g | ∃ i, g = C (f.coeff i)}
state_after: R : Type u
S : Type v
T : Type w
ι : Type x
k : Type y
A : Type z
a b : R
m n✝ : ℕ
inst✝ : Semiring R
p✝ q r f : R[X]
I : Ideal R[X]
p : Ideal R[X] := Ideal.span {g | ∃ i, g = C (f.coeff i)}
n : ℕ
_hn : n ∈ f.support
⊢ C (f.coeff n) * X ^ n ∈ Ideal.span {g | ∃ i, g = C (f.coeff i)}
tactic: dsimp
state_before: R : Type u
S : Type v
T : Type w
ι : Type x
k : Type y
A : Type z
a b : R
m n✝ : ℕ
inst✝ : Semiring R
p✝ q r f : R[X]
I : Ideal R[X]
p : Ideal R[X] := Ideal.span {g | ∃ i, g = C (f.coeff i)}
n : ℕ
_hn : n ∈ f.support
⊢ C (f.coeff n) * X ^ n ∈ Ideal.span {g | ∃ i, g = C (f.coeff i)}
state_after: R : Type u
S : Type v
T : Type w
ι : Type x
k : Type y
A : Type z
a b : R
m n✝ : ℕ
inst✝ : Semiring R
p✝ q r f : R[X]
I : Ideal R[X]
p : Ideal R[X] := Ideal.span {g | ∃ i, g = C (f.coeff i)}
n : ℕ
_hn : n ∈ f.support
this : C (f.coeff n) ∈ p
⊢ C (f.coeff n) * X ^ n ∈ Ideal.span {g | ∃ i, g = C (f.coeff i)}
tactic: have : C (coeff f n) ∈ p := by
    apply subset_span
    rw [mem_setOf_eq]
    use n
state_before: R : Type u
S : Type v
T : Type w
ι : Type x
k : Type y
A : Type z
a b : R
m n✝ : ℕ
inst✝ : Semiring R
p✝ q r f : R[X]
I : Ideal R[X]
p : Ideal R[X] := Ideal.span {g | ∃ i, g = C (f.coeff i)}
n : ℕ
_hn : n ∈ f.support
this : C (f.coeff n) ∈ p
⊢ C (f.coeff n) * X ^ n ∈ Ideal.span {g | ∃ i, g = C (f.coeff i)}
state_after: R : Type u
S : Type v
T : Type w
ι : Type x
k : Type y
A : Type z
a b : R
m n✝ : ℕ
inst✝ : Semiring R
p✝ q r f : R[X]
I : Ideal R[X]
p : Ideal R[X] := Ideal.span {g | ∃ i, g = C (f.coeff i)}
n : ℕ
_hn : n ∈ f.support
this✝ : C (f.coeff n) ∈ p
this : (monomial n) 1 • C (f.coeff n) ∈ p
⊢ C (f.coeff n) * X ^ n ∈ Ideal.span {g | ∃ i, g = C (f.coeff i)}
tactic: have : monomial n (1 : R) • C (coeff f n) ∈ p := p.smul_mem _ this
state_before: R : Type u
S : Type v
T : Type w
ι : Type x
k : Type y
A : Type z
a b : R
m n✝ : ℕ
inst✝ : Semiring R
p✝ q r f : R[X]
I : Ideal R[X]
p : Ideal R[X] := Ideal.span {g | ∃ i, g = C (f.coeff i)}
n : ℕ
_hn : n ∈ f.support
this✝ : C (f.coeff n) ∈ p
this : (monomial n) 1 • C (f.coeff n) ∈ p
⊢ C (f.coeff n) * X ^ n ∈ Ideal.span {g | ∃ i, g = C (f.coeff i)}
state_after: case h.e'_4
R : Type u
S : Type v
T : Type w
ι : Type x
k : Type y
A : Type z
a b : R
m n✝ : ℕ
inst✝ : Semiring R
p✝ q r f : R[X]
I : Ideal R[X]
p : Ideal R[X] := Ideal.span {g | ∃ i, g = C (f.coeff i)}
n : ℕ
_hn : n ∈ f.support
this✝ : C (f.coeff n) ∈ p
this : (monomial n) 1 • C (f.coeff n) ∈ p
⊢ C (f.coeff n) * X ^ n = (monomial n) 1 • C (f.coeff n)
tactic: convert this using 1
state_before: case h.e'_4
R : Type u
S : Type v
T : Type w
ι : Type x
k : Type y
A : Type z
a b : R
m n✝ : ℕ
inst✝ : Semiring R
p✝ q r f : R[X]
I : Ideal R[X]
p : Ideal R[X] := Ideal.span {g | ∃ i, g = C (f.coeff i)}
n : ℕ
_hn : n ∈ f.support
this✝ : C (f.coeff n) ∈ p
this : (monomial n) 1 • C (f.coeff n) ∈ p
⊢ C (f.coeff n) * X ^ n = (monomial n) 1 • C (f.coeff n)
state_after: case h.e'_4
R : Type u
S : Type v
T : Type w
ι : Type x
k : Type y
A : Type z
a b : R
m n✝ : ℕ
inst✝ : Semiring R
p✝ q r f : R[X]
I : Ideal R[X]
p : Ideal R[X] := Ideal.span {g | ∃ i, g = C (f.coeff i)}
n : ℕ
_hn : n ∈ f.support
this✝ : C (f.coeff n) ∈ p
this : (monomial n) 1 • C (f.coeff n) ∈ p
⊢ C (f.coeff n) * X ^ n = (monomial n) (f.coeff n)
tactic: simp only [monomial_mul_C, one_mul, smul_eq_mul]
state_before: case h.e'_4
R : Type u
S : Type v
T : Type w
ι : Type x
k : Type y
A : Type z
a b : R
m n✝ : ℕ
inst✝ : Semiring R
p✝ q r f : R[X]
I : Ideal R[X]
p : Ideal R[X] := Ideal.span {g | ∃ i, g = C (f.coeff i)}
n : ℕ
_hn : n ∈ f.support
this✝ : C (f.coeff n) ∈ p
this : (monomial n) 1 • C (f.coeff n) ∈ p
⊢ C (f.coeff n) * X ^ n = (monomial n) (f.coeff n)
state_after: no goals
tactic: rw [← C_mul_X_pow_eq_monomial]