-- Mathlib/Analysis/CStarAlgebra/ContinuousFunctionalCalculus/NonUnital.lean
lemma cfcₙ_sub : cfcₙ (fun x ↦ f x - g x) a = cfcₙ f a - cfcₙ g a

Proof state:
R : Type u_1
A : Type u_2
p : A → Prop
inst✝¹² : CommRing R
inst✝¹¹ : Nontrivial R
inst✝¹⁰ : StarRing R
inst✝⁹ : MetricSpace R
inst✝⁸ : IsTopologicalRing R
inst✝⁷ : ContinuousStar R
inst✝⁶ : TopologicalSpace A
inst✝⁵ : NonUnitalRing A
inst✝⁴ : StarRing A
inst✝³ : Module R A
inst✝² : IsScalarTower R A A
inst✝¹ : SMulCommClass R A A
inst✝ : NonUnitalContinuousFunctionalCalculus R p
f g : R → R
a : A
hf : autoParam (ContinuousOn f (σₙ R a)) _auto✝
hf0 : autoParam (f 0 = 0) _auto✝
hg : autoParam (ContinuousOn g (σₙ R a)) _auto✝
hg0 : autoParam (g 0 = 0) _auto✝
⊢ cfcₙ (fun x => f x - g x) a = cfcₙ f a - cfcₙ g a

Tactic:
by_cases ha : p a

Result:
case pos
R : Type u_1
A : Type u_2
p : A → Prop
inst✝¹² : CommRing R
inst✝¹¹ : Nontrivial R
inst✝¹⁰ : StarRing R
inst✝⁹ : MetricSpace R
inst✝⁸ : IsTopologicalRing R
inst✝⁷ : ContinuousStar R
inst✝⁶ : TopologicalSpace A
inst✝⁵ : NonUnitalRing A
inst✝⁴ : StarRing A
inst✝³ : Module R A
inst✝² : IsScalarTower R A A
inst✝¹ : SMulCommClass R A A
inst✝ : NonUnitalContinuousFunctionalCalculus R p
f g : R → R
a : A
hf : autoParam (ContinuousOn f (σₙ R a)) _auto✝
hf0 : autoParam (f 0 = 0) _auto✝
hg : autoParam (ContinuousOn g (σₙ R a)) _auto✝
hg0 : autoParam (g 0 = 0) _auto✝
ha : p a
⊢ cfcₙ (fun x => f x - g x) a = cfcₙ f a - cfcₙ g a

case neg
R : Type u_1
A : Type u_2
p : A → Prop
inst✝¹² : CommRing R
inst✝¹¹ : Nontrivial R
inst✝¹⁰ : StarRing R
inst✝⁹ : MetricSpace R
inst✝⁸ : IsTopologicalRing R
inst✝⁷ : ContinuousStar R
inst✝⁶ : TopologicalSpace A
inst✝⁵ : NonUnitalRing A
inst✝⁴ : StarRing A
inst✝³ : Module R A
inst✝² : IsScalarTower R A A
inst✝¹ : SMulCommClass R A A
inst✝ : NonUnitalContinuousFunctionalCalculus R p
f g : R → R
a : A
hf : autoParam (ContinuousOn f (σₙ R a)) _auto✝
hf0 : autoParam (f 0 = 0) _auto✝
hg : autoParam (ContinuousOn g (σₙ R a)) _auto✝
hg0 : autoParam (g 0 = 0) _auto✝
ha : ¬p a
⊢ cfcₙ (fun x => f x - g x) a = cfcₙ f a - cfcₙ g a

Proof state:
case neg
R : Type u_1
A : Type u_2
p : A → Prop
inst✝¹² : CommRing R
inst✝¹¹ : Nontrivial R
inst✝¹⁰ : StarRing R
inst✝⁹ : MetricSpace R
inst✝⁸ : IsTopologicalRing R
inst✝⁷ : ContinuousStar R
inst✝⁶ : TopologicalSpace A
inst✝⁵ : NonUnitalRing A
inst✝⁴ : StarRing A
inst✝³ : Module R A
inst✝² : IsScalarTower R A A
inst✝¹ : SMulCommClass R A A
inst✝ : NonUnitalContinuousFunctionalCalculus R p
f g : R → R
a : A
hf : autoParam (ContinuousOn f (σₙ R a)) _auto✝
hf0 : autoParam (f 0 = 0) _auto✝
hg : autoParam (ContinuousOn g (σₙ R a)) _auto✝
hg0 : autoParam (g 0 = 0) _auto✝
ha : ¬p a
⊢ cfcₙ (fun x => f x - g x) a = cfcₙ f a - cfcₙ g a

Tactic:
simp [cfcₙ_apply_of_not_predicate a ha]

Result:
no goals

Proof state:
case pos
R : Type u_1
A : Type u_2
p : A → Prop
inst✝¹² : CommRing R
inst✝¹¹ : Nontrivial R
inst✝¹⁰ : StarRing R
inst✝⁹ : MetricSpace R
inst✝⁸ : IsTopologicalRing R
inst✝⁷ : ContinuousStar R
inst✝⁶ : TopologicalSpace A
inst✝⁵ : NonUnitalRing A
inst✝⁴ : StarRing A
inst✝³ : Module R A
inst✝² : IsScalarTower R A A
inst✝¹ : SMulCommClass R A A
inst✝ : NonUnitalContinuousFunctionalCalculus R p
f g : R → R
a : A
hf : autoParam (ContinuousOn f (σₙ R a)) _auto✝
hf0 : autoParam (f 0 = 0) _auto✝
hg : autoParam (ContinuousOn g (σₙ R a)) _auto✝
hg0 : autoParam (g 0 = 0) _auto✝
ha : p a
⊢ (cfcₙHom ha) { toFun := (σₙ R a).restrict fun x => f x - g x, continuous_toFun := ⋯, map_zero' := ⋯ } =
    (cfcₙHom ha)
      ({ toFun := (σₙ R a).restrict f, continuous_toFun := ⋯, map_zero' := ⋯ } -
        { toFun := (σₙ R a).restrict g, continuous_toFun := ⋯, map_zero' := ⋯ })

Tactic:
congr

Result:
no goals

Proof state:
case pos
R : Type u_1
A : Type u_2
p : A → Prop
inst✝¹² : CommRing R
inst✝¹¹ : Nontrivial R
inst✝¹⁰ : StarRing R
inst✝⁹ : MetricSpace R
inst✝⁸ : IsTopologicalRing R
inst✝⁷ : ContinuousStar R
inst✝⁶ : TopologicalSpace A
inst✝⁵ : NonUnitalRing A
inst✝⁴ : StarRing A
inst✝³ : Module R A
inst✝² : IsScalarTower R A A
inst✝¹ : SMulCommClass R A A
inst✝ : NonUnitalContinuousFunctionalCalculus R p
f g : R → R
a : A
hf : autoParam (ContinuousOn f (σₙ R a)) _auto✝
hf0 : autoParam (f 0 = 0) _auto✝
hg : autoParam (ContinuousOn g (σₙ R a)) _auto✝
hg0 : autoParam (g 0 = 0) _auto✝
ha : p a
⊢ cfcₙ (fun x => f x - g x) a = cfcₙ f a - cfcₙ g a

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

Result:
case pos
R : Type u_1
A : Type u_2
p : A → Prop
inst✝¹² : CommRing R
inst✝¹¹ : Nontrivial R
inst✝¹⁰ : StarRing R
inst✝⁹ : MetricSpace R
inst✝⁸ : IsTopologicalRing R
inst✝⁷ : ContinuousStar R
inst✝⁶ : TopologicalSpace A
inst✝⁵ : NonUnitalRing A
inst✝⁴ : StarRing A
inst✝³ : Module R A
inst✝² : IsScalarTower R A A
inst✝¹ : SMulCommClass R A A
inst✝ : NonUnitalContinuousFunctionalCalculus R p
f g : R → R
a : A
hf : autoParam (ContinuousOn f (σₙ R a)) _auto✝
hf0 : autoParam (f 0 = 0) _auto✝
hg : autoParam (ContinuousOn g (σₙ R a)) _auto✝
hg0 : autoParam (g 0 = 0) _auto✝
ha : p a
⊢ (cfcₙHom ha) { toFun := (σₙ R a).restrict fun x => f x - g x, continuous_toFun := ⋯, map_zero' := ⋯ } =
    (cfcₙHom ha)
      ({ toFun := (σₙ R a).restrict f, continuous_toFun := ⋯, map_zero' := ⋯ } -
        { toFun := (σₙ R a).restrict g, continuous_toFun := ⋯, map_zero' := ⋯ })