Theorem: Polynomial.span_singleton_annIdealGenerator
File: Mathlib/LinearAlgebra/AnnihilatingPolynomial.lean

tactic: by_cases h : annIdealGenerator 𝕜 a = 0
state_before: 𝕜 : Type u_1
A : Type u_2
inst✝² : Field 𝕜
inst✝¹ : Ring A
inst✝ : Algebra 𝕜 A
a : A
⊢ Ideal.span {annIdealGenerator 𝕜 a} = annIdeal 𝕜 a
state_after: case pos
𝕜 : Type u_1
A : Type u_2
inst✝² : Field 𝕜
inst✝¹ : Ring A
inst✝ : Algebra 𝕜 A
a : A
h : annIdealGenerator 𝕜 a = 0
⊢ Ideal.span {annIdealGenerator 𝕜 a} = annIdeal 𝕜 a

case neg
𝕜 : Type u_1
A : Type u_2
inst✝² : Field 𝕜
inst✝¹ : Ring A
inst✝ : Algebra 𝕜 A
a : A
h : ¬annIdealGenerator 𝕜 a = 0
⊢ Ideal.span {annIdealGenerator 𝕜 a} = annIdeal 𝕜 a

tactic: rw [h, annIdealGenerator_eq_zero_iff.mp h, Set.singleton_zero, Ideal.span_zero]
state_before: case pos
𝕜 : Type u_1
A : Type u_2
inst✝² : Field 𝕜
inst✝¹ : Ring A
inst✝ : Algebra 𝕜 A
a : A
h : annIdealGenerator 𝕜 a = 0
⊢ Ideal.span {annIdealGenerator 𝕜 a} = annIdeal 𝕜 a
state_after: no goals

tactic: rw [annIdealGenerator, Ideal.span_singleton_mul_right_unit, Ideal.span_singleton_generator]
state_before: case neg
𝕜 : Type u_1
A : Type u_2
inst✝² : Field 𝕜
inst✝¹ : Ring A
inst✝ : Algebra 𝕜 A
a : A
h : ¬annIdealGenerator 𝕜 a = 0
⊢ Ideal.span {annIdealGenerator 𝕜 a} = annIdeal 𝕜 a
state_after: case neg.h2
𝕜 : Type u_1
A : Type u_2
inst✝² : Field 𝕜
inst✝¹ : Ring A
inst✝ : Algebra 𝕜 A
a : A
h : ¬annIdealGenerator 𝕜 a = 0
⊢ IsUnit (C (IsPrincipal.generator (annIdeal 𝕜 a)).leadingCoeff⁻¹)

tactic: apply Polynomial.isUnit_C.mpr
state_before: case neg.h2
𝕜 : Type u_1
A : Type u_2
inst✝² : Field 𝕜
inst✝¹ : Ring A
inst✝ : Algebra 𝕜 A
a : A
h : ¬annIdealGenerator 𝕜 a = 0
⊢ IsUnit (C (IsPrincipal.generator (annIdeal 𝕜 a)).leadingCoeff⁻¹)
state_after: case neg.h2
𝕜 : Type u_1
A : Type u_2
inst✝² : Field 𝕜
inst✝¹ : Ring A
inst✝ : Algebra 𝕜 A
a : A
h : ¬annIdealGenerator 𝕜 a = 0
⊢ IsUnit (IsPrincipal.generator (annIdeal 𝕜 a)).leadingCoeff⁻¹

tactic: apply IsUnit.mk0
state_before: case neg.h2
𝕜 : Type u_1
A : Type u_2
inst✝² : Field 𝕜
inst✝¹ : Ring A
inst✝ : Algebra 𝕜 A
a : A
h : ¬annIdealGenerator 𝕜 a = 0
⊢ IsUnit (IsPrincipal.generator (annIdeal 𝕜 a)).leadingCoeff⁻¹
state_after: case neg.h2.hx
𝕜 : Type u_1
A : Type u_2
inst✝² : Field 𝕜
inst✝¹ : Ring A
inst✝ : Algebra 𝕜 A
a : A
h : ¬annIdealGenerator 𝕜 a = 0
⊢ (IsPrincipal.generator (annIdeal 𝕜 a)).leadingCoeff⁻¹ ≠ 0

tactic: apply inv_eq_zero.not.mpr
state_before: case neg.h2.hx
𝕜 : Type u_1
A : Type u_2
inst✝² : Field 𝕜
inst✝¹ : Ring A
inst✝ : Algebra 𝕜 A
a : A
h : ¬annIdealGenerator 𝕜 a = 0
⊢ (IsPrincipal.generator (annIdeal 𝕜 a)).leadingCoeff⁻¹ ≠ 0
state_after: case neg.h2.hx
𝕜 : Type u_1
A : Type u_2
inst✝² : Field 𝕜
inst✝¹ : Ring A
inst✝ : Algebra 𝕜 A
a : A
h : ¬annIdealGenerator 𝕜 a = 0
⊢ ¬(IsPrincipal.generator (annIdeal 𝕜 a)).leadingCoeff = 0

tactic: apply Polynomial.leadingCoeff_eq_zero.not.mpr
state_before: case neg.h2.hx
𝕜 : Type u_1
A : Type u_2
inst✝² : Field 𝕜
inst✝¹ : Ring A
inst✝ : Algebra 𝕜 A
a : A
h : ¬annIdealGenerator 𝕜 a = 0
⊢ ¬(IsPrincipal.generator (annIdeal 𝕜 a)).leadingCoeff = 0
state_after: case neg.h2.hx
𝕜 : Type u_1
A : Type u_2
inst✝² : Field 𝕜
inst✝¹ : Ring A
inst✝ : Algebra 𝕜 A
a : A
h : ¬annIdealGenerator 𝕜 a = 0
⊢ ¬IsPrincipal.generator (annIdeal 𝕜 a) = 0

tactic: apply (mul_ne_zero_iff.mp h).1
state_before: case neg.h2.hx
𝕜 : Type u_1
A : Type u_2
inst✝² : Field 𝕜
inst✝¹ : Ring A
inst✝ : Algebra 𝕜 A
a : A
h : ¬annIdealGenerator 𝕜 a = 0
⊢ ¬IsPrincipal.generator (annIdeal 𝕜 a) = 0
state_after: no goals