Theorem: Field.finSepDegree_eq
File: Mathlib/FieldTheory/PurelyInseparable.lean

tactic: have : Algebra.IsAlgebraic (separableClosure F E) E := Algebra.IsAlgebraic.tower_top (K := F) _
state_before: F : Type u
E : Type v
inst✝⁵ : Field F
inst✝⁴ : Field E
inst✝³ : Algebra F E
K : Type w
inst✝² : Field K
inst✝¹ : Algebra F K
inst✝ : Algebra.IsAlgebraic F E
⊢ finSepDegree F E = Cardinal.toNat (sepDegree F E)
state_after: F : Type u
E : Type v
inst✝⁵ : Field F
inst✝⁴ : Field E
inst✝³ : Algebra F E
K : Type w
inst✝² : Field K
inst✝¹ : Algebra F K
inst✝ : Algebra.IsAlgebraic F E
this : Algebra.IsAlgebraic (↥(separableClosure F E)) E
⊢ finSepDegree F E = Cardinal.toNat (sepDegree F E)

tactic: have h := finSepDegree_mul_finSepDegree_of_isAlgebraic F (separableClosure F E) E |>.symm
state_before: F : Type u
E : Type v
inst✝⁵ : Field F
inst✝⁴ : Field E
inst✝³ : Algebra F E
K : Type w
inst✝² : Field K
inst✝¹ : Algebra F K
inst✝ : Algebra.IsAlgebraic F E
this : Algebra.IsAlgebraic (↥(separableClosure F E)) E
⊢ finSepDegree F E = Cardinal.toNat (sepDegree F E)
state_after: F : Type u
E : Type v
inst✝⁵ : Field F
inst✝⁴ : Field E
inst✝³ : Algebra F E
K : Type w
inst✝² : Field K
inst✝¹ : Algebra F K
inst✝ : Algebra.IsAlgebraic F E
this : Algebra.IsAlgebraic (↥(separableClosure F E)) E
h : finSepDegree F E = finSepDegree F ↥(separableClosure F E) * finSepDegree (↥(separableClosure F E)) E
⊢ finSepDegree F E = Cardinal.toNat (sepDegree F E)

tactic: haveI := separableClosure.isSeparable F E
state_before: F : Type u
E : Type v
inst✝⁵ : Field F
inst✝⁴ : Field E
inst✝³ : Algebra F E
K : Type w
inst✝² : Field K
inst✝¹ : Algebra F K
inst✝ : Algebra.IsAlgebraic F E
this : Algebra.IsAlgebraic (↥(separableClosure F E)) E
h : finSepDegree F E = finSepDegree F ↥(separableClosure F E) * finSepDegree (↥(separableClosure F E)) E
⊢ finSepDegree F E = Cardinal.toNat (sepDegree F E)
state_after: F : Type u
E : Type v
inst✝⁵ : Field F
inst✝⁴ : Field E
inst✝³ : Algebra F E
K : Type w
inst✝² : Field K
inst✝¹ : Algebra F K
inst✝ : Algebra.IsAlgebraic F E
this✝ : Algebra.IsAlgebraic (↥(separableClosure F E)) E
h : finSepDegree F E = finSepDegree F ↥(separableClosure F E) * finSepDegree (↥(separableClosure F E)) E
this : IsSeparable F ↥(separableClosure F E)
⊢ finSepDegree F E = Cardinal.toNat (sepDegree F E)

tactic: haveI := separableClosure.isPurelyInseparable F E
state_before: F : Type u
E : Type v
inst✝⁵ : Field F
inst✝⁴ : Field E
inst✝³ : Algebra F E
K : Type w
inst✝² : Field K
inst✝¹ : Algebra F K
inst✝ : Algebra.IsAlgebraic F E
this✝ : Algebra.IsAlgebraic (↥(separableClosure F E)) E
h : finSepDegree F E = finSepDegree F ↥(separableClosure F E) * finSepDegree (↥(separableClosure F E)) E
this : IsSeparable F ↥(separableClosure F E)
⊢ finSepDegree F E = Cardinal.toNat (sepDegree F E)
state_after: F : Type u
E : Type v
inst✝⁵ : Field F
inst✝⁴ : Field E
inst✝³ : Algebra F E
K : Type w
inst✝² : Field K
inst✝¹ : Algebra F K
inst✝ : Algebra.IsAlgebraic F E
this✝¹ : Algebra.IsAlgebraic (↥(separableClosure F E)) E
h : finSepDegree F E = finSepDegree F ↥(separableClosure F E) * finSepDegree (↥(separableClosure F E)) E
this✝ : IsSeparable F ↥(separableClosure F E)
this : IsPurelyInseparable (↥(separableClosure F E)) E
⊢ finSepDegree F E = Cardinal.toNat (sepDegree F E)

tactic: rwa [finSepDegree_eq_finrank_of_isSeparable F (separableClosure F E),
  IsPurelyInseparable.finSepDegree_eq_one (separableClosure F E) E, mul_one] at h
state_before: F : Type u
E : Type v
inst✝⁵ : Field F
inst✝⁴ : Field E
inst✝³ : Algebra F E
K : Type w
inst✝² : Field K
inst✝¹ : Algebra F K
inst✝ : Algebra.IsAlgebraic F E
this✝¹ : Algebra.IsAlgebraic (↥(separableClosure F E)) E
h : finSepDegree F E = finSepDegree F ↥(separableClosure F E) * finSepDegree (↥(separableClosure F E)) E
this✝ : IsSeparable F ↥(separableClosure F E)
this : IsPurelyInseparable (↥(separableClosure F E)) E
⊢ finSepDegree F E = Cardinal.toNat (sepDegree F E)
state_after: no goals