-- Mathlib/Analysis/CStarAlgebra/ContinuousFunctionalCalculus/Unital.lean
lemma cfc_sub : cfc (fun x ↦ f x - g x) a = cfc f a - cfc g a

Proof state:
R : Type u_1
A : Type u_2
p : A → Prop
inst✝⁹ : CommRing R
inst✝⁸ : StarRing R
inst✝⁷ : MetricSpace R
inst✝⁶ : IsTopologicalRing R
inst✝⁵ : ContinuousStar R
inst✝⁴ : TopologicalSpace A
inst✝³ : Ring A
inst✝² : StarRing A
inst✝¹ : Algebra R A
inst✝ : ContinuousFunctionalCalculus R p
f g : R → R
a : A
hf : autoParam (ContinuousOn f (spectrum R a)) _auto✝
hg : autoParam (ContinuousOn g (spectrum R a)) _auto✝
⊢ cfc (fun x => f x - g x) a = cfc f a - cfc g a

Tactic:
by_cases ha : p a

Result:
case pos
R : Type u_1
A : Type u_2
p : A → Prop
inst✝⁹ : CommRing R
inst✝⁸ : StarRing R
inst✝⁷ : MetricSpace R
inst✝⁶ : IsTopologicalRing R
inst✝⁵ : ContinuousStar R
inst✝⁴ : TopologicalSpace A
inst✝³ : Ring A
inst✝² : StarRing A
inst✝¹ : Algebra R A
inst✝ : ContinuousFunctionalCalculus R p
f g : R → R
a : A
hf : autoParam (ContinuousOn f (spectrum R a)) _auto✝
hg : autoParam (ContinuousOn g (spectrum R a)) _auto✝
ha : p a
⊢ cfc (fun x => f x - g x) a = cfc f a - cfc g a

case neg
R : Type u_1
A : Type u_2
p : A → Prop
inst✝⁹ : CommRing R
inst✝⁸ : StarRing R
inst✝⁷ : MetricSpace R
inst✝⁶ : IsTopologicalRing R
inst✝⁵ : ContinuousStar R
inst✝⁴ : TopologicalSpace A
inst✝³ : Ring A
inst✝² : StarRing A
inst✝¹ : Algebra R A
inst✝ : ContinuousFunctionalCalculus R p
f g : R → R
a : A
hf : autoParam (ContinuousOn f (spectrum R a)) _auto✝
hg : autoParam (ContinuousOn g (spectrum R a)) _auto✝
ha : ¬p a
⊢ cfc (fun x => f x - g x) a = cfc f a - cfc g a

Proof state:
case pos
R : Type u_1
A : Type u_2
p : A → Prop
inst✝⁹ : CommRing R
inst✝⁸ : StarRing R
inst✝⁷ : MetricSpace R
inst✝⁶ : IsTopologicalRing R
inst✝⁵ : ContinuousStar R
inst✝⁴ : TopologicalSpace A
inst✝³ : Ring A
inst✝² : StarRing A
inst✝¹ : Algebra R A
inst✝ : ContinuousFunctionalCalculus R p
f g : R → R
a : A
hf : autoParam (ContinuousOn f (spectrum R a)) _auto✝
hg : autoParam (ContinuousOn g (spectrum R a)) _auto✝
ha : p a
⊢ (cfcHom ha) { toFun := (spectrum R a).restrict fun x => f x - g x, continuous_toFun := ⋯ } =
    (cfcHom ha)
      ({ toFun := (spectrum R a).restrict f, continuous_toFun := ⋯ } -
        { toFun := (spectrum R a).restrict g, continuous_toFun := ⋯ })

Tactic:
congr

Result:
no goals

Proof state:
case pos
R : Type u_1
A : Type u_2
p : A → Prop
inst✝⁹ : CommRing R
inst✝⁸ : StarRing R
inst✝⁷ : MetricSpace R
inst✝⁶ : IsTopologicalRing R
inst✝⁵ : ContinuousStar R
inst✝⁴ : TopologicalSpace A
inst✝³ : Ring A
inst✝² : StarRing A
inst✝¹ : Algebra R A
inst✝ : ContinuousFunctionalCalculus R p
f g : R → R
a : A
hf : autoParam (ContinuousOn f (spectrum R a)) _auto✝
hg : autoParam (ContinuousOn g (spectrum R a)) _auto✝
ha : p a
⊢ cfc (fun x => f x - g x) a = cfc f a - cfc g a

Tactic:
rw [cfc_apply f a, cfc_apply g a, ← map_sub, cfc_apply ..]

Result:
case pos
R : Type u_1
A : Type u_2
p : A → Prop
inst✝⁹ : CommRing R
inst✝⁸ : StarRing R
inst✝⁷ : MetricSpace R
inst✝⁶ : IsTopologicalRing R
inst✝⁵ : ContinuousStar R
inst✝⁴ : TopologicalSpace A
inst✝³ : Ring A
inst✝² : StarRing A
inst✝¹ : Algebra R A
inst✝ : ContinuousFunctionalCalculus R p
f g : R → R
a : A
hf : autoParam (ContinuousOn f (spectrum R a)) _auto✝
hg : autoParam (ContinuousOn g (spectrum R a)) _auto✝
ha : p a
⊢ (cfcHom ha) { toFun := (spectrum R a).restrict fun x => f x - g x, continuous_toFun := ⋯ } =
    (cfcHom ha)
      ({ toFun := (spectrum R a).restrict f, continuous_toFun := ⋯ } -
        { toFun := (spectrum R a).restrict g, continuous_toFun := ⋯ })

Proof state:
case neg
R : Type u_1
A : Type u_2
p : A → Prop
inst✝⁹ : CommRing R
inst✝⁸ : StarRing R
inst✝⁷ : MetricSpace R
inst✝⁶ : IsTopologicalRing R
inst✝⁵ : ContinuousStar R
inst✝⁴ : TopologicalSpace A
inst✝³ : Ring A
inst✝² : StarRing A
inst✝¹ : Algebra R A
inst✝ : ContinuousFunctionalCalculus R p
f g : R → R
a : A
hf : autoParam (ContinuousOn f (spectrum R a)) _auto✝
hg : autoParam (ContinuousOn g (spectrum R a)) _auto✝
ha : ¬p a
⊢ cfc (fun x => f x - g x) a = cfc f a - cfc g a

Tactic:
simp [cfc_apply_of_not_predicate a ha]

Result:
no goals