-- Mathlib/Analysis/CStarAlgebra/ContinuousFunctionalCalculus/Isometric.lean
lemma nnnorm_cfc_nnreal_lt {f : ℝ≥0 → ℝ≥0} {a : A} {c : ℝ≥0} (hc : 0 < c)
    (h : ∀ x ∈ σ ℝ≥0 a, f x < c) : ‖cfc f a‖₊ < c

Proof state:
A : Type u_1
inst✝⁶ : NormedRing A
inst✝⁵ : StarRing A
inst✝⁴ : NormedAlgebra ℝ A
inst✝³ : PartialOrder A
inst✝² : StarOrderedRing A
inst✝¹ : IsometricContinuousFunctionalCalculus ℝ A IsSelfAdjoint
inst✝ : NonnegSpectrumClass ℝ A
f : ℝ≥0 → ℝ≥0
a : A
c : ℝ≥0
hc : 0 < c
h : ∀ x ∈ σ ℝ≥0 a, f x < c
⊢ ‖cfc f a‖₊ < c

Tactic:
obtain (_ | _) := subsingleton_or_nontrivial A

Result:
case inl
A : Type u_1
inst✝⁶ : NormedRing A
inst✝⁵ : StarRing A
inst✝⁴ : NormedAlgebra ℝ A
inst✝³ : PartialOrder A
inst✝² : StarOrderedRing A
inst✝¹ : IsometricContinuousFunctionalCalculus ℝ A IsSelfAdjoint
inst✝ : NonnegSpectrumClass ℝ A
f : ℝ≥0 → ℝ≥0
a : A
c : ℝ≥0
hc : 0 < c
h : ∀ x ∈ σ ℝ≥0 a, f x < c
h✝ : Subsingleton A
⊢ ‖cfc f a‖₊ < c

case inr
A : Type u_1
inst✝⁶ : NormedRing A
inst✝⁵ : StarRing A
inst✝⁴ : NormedAlgebra ℝ A
inst✝³ : PartialOrder A
inst✝² : StarOrderedRing A
inst✝¹ : IsometricContinuousFunctionalCalculus ℝ A IsSelfAdjoint
inst✝ : NonnegSpectrumClass ℝ A
f : ℝ≥0 → ℝ≥0
a : A
c : ℝ≥0
hc : 0 < c
h : ∀ x ∈ σ ℝ≥0 a, f x < c
h✝ : Nontrivial A
⊢ ‖cfc f a‖₊ < c

Proof state:
case inr.intro.intro
A : Type u_1
inst✝⁶ : NormedRing A
inst✝⁵ : StarRing A
inst✝⁴ : NormedAlgebra ℝ A
inst✝³ : PartialOrder A
inst✝² : StarOrderedRing A
inst✝¹ : IsometricContinuousFunctionalCalculus ℝ A IsSelfAdjoint
inst✝ : NonnegSpectrumClass ℝ A
f : ℝ≥0 → ℝ≥0
a : A
c : ℝ≥0
hc : 0 < c
h : ∀ x ∈ σ ℝ≥0 a, f x < c
h✝ : Nontrivial A
hf : ContinuousOn f (σ ℝ≥0 a)
ha : 0 ≤ a
x : ℝ≥0
hx : x ∈ σ ℝ≥0 a
⊢ f x < c

Tactic:
exact h x hx

Result:
no goals

Proof state:
A : Type u_1
inst✝⁶ : NormedRing A
inst✝⁵ : StarRing A
inst✝⁴ : NormedAlgebra ℝ A
inst✝³ : PartialOrder A
inst✝² : StarOrderedRing A
inst✝¹ : IsometricContinuousFunctionalCalculus ℝ A IsSelfAdjoint
inst✝ : NonnegSpectrumClass ℝ A
f : ℝ≥0 → ℝ≥0
a : A
c : ℝ≥0
hc : 0 < c
h : ∀ x ∈ σ ℝ≥0 a, f x < c
h✝ : Nontrivial A
⊢ (fun x => ‖x‖₊ < c) 0

Tactic:
simpa

Result:
no goals

Proof state:
case inl
A : Type u_1
inst✝⁶ : NormedRing A
inst✝⁵ : StarRing A
inst✝⁴ : NormedAlgebra ℝ A
inst✝³ : PartialOrder A
inst✝² : StarOrderedRing A
inst✝¹ : IsometricContinuousFunctionalCalculus ℝ A IsSelfAdjoint
inst✝ : NonnegSpectrumClass ℝ A
f : ℝ≥0 → ℝ≥0
a : A
c : ℝ≥0
hc : 0 < c
h : ∀ x ∈ σ ℝ≥0 a, f x < c
h✝ : Subsingleton A
⊢ ‖0‖₊ < c

Tactic:
simpa

Result:
no goals

Proof state:
case inl
A : Type u_1
inst✝⁶ : NormedRing A
inst✝⁵ : StarRing A
inst✝⁴ : NormedAlgebra ℝ A
inst✝³ : PartialOrder A
inst✝² : StarOrderedRing A
inst✝¹ : IsometricContinuousFunctionalCalculus ℝ A IsSelfAdjoint
inst✝ : NonnegSpectrumClass ℝ A
f : ℝ≥0 → ℝ≥0
a : A
c : ℝ≥0
hc : 0 < c
h : ∀ x ∈ σ ℝ≥0 a, f x < c
h✝ : Subsingleton A
⊢ ‖cfc f a‖₊ < c

Tactic:
rw [Subsingleton.elim (cfc f a) 0]

Result:
case inl
A : Type u_1
inst✝⁶ : NormedRing A
inst✝⁵ : StarRing A
inst✝⁴ : NormedAlgebra ℝ A
inst✝³ : PartialOrder A
inst✝² : StarOrderedRing A
inst✝¹ : IsometricContinuousFunctionalCalculus ℝ A IsSelfAdjoint
inst✝ : NonnegSpectrumClass ℝ A
f : ℝ≥0 → ℝ≥0
a : A
c : ℝ≥0
hc : 0 < c
h : ∀ x ∈ σ ℝ≥0 a, f x < c
h✝ : Subsingleton A
⊢ ‖0‖₊ < c

Proof state:
case inr
A : Type u_1
inst✝⁶ : NormedRing A
inst✝⁵ : StarRing A
inst✝⁴ : NormedAlgebra ℝ A
inst✝³ : PartialOrder A
inst✝² : StarOrderedRing A
inst✝¹ : IsometricContinuousFunctionalCalculus ℝ A IsSelfAdjoint
inst✝ : NonnegSpectrumClass ℝ A
f : ℝ≥0 → ℝ≥0
a : A
c : ℝ≥0
hc : 0 < c
h : ∀ x ∈ σ ℝ≥0 a, f x < c
h✝ : Nontrivial A
hf : ContinuousOn f (σ ℝ≥0 a)
ha : 0 ≤ a
⊢ ∀ x ∈ f '' σ ℝ≥0 a, x < c

Tactic:
rintro - ⟨x, hx, rfl⟩

Result:
case inr.intro.intro
A : Type u_1
inst✝⁶ : NormedRing A
inst✝⁵ : StarRing A
inst✝⁴ : NormedAlgebra ℝ A
inst✝³ : PartialOrder A
inst✝² : StarOrderedRing A
inst✝¹ : IsometricContinuousFunctionalCalculus ℝ A IsSelfAdjoint
inst✝ : NonnegSpectrumClass ℝ A
f : ℝ≥0 → ℝ≥0
a : A
c : ℝ≥0
hc : 0 < c
h : ∀ x ∈ σ ℝ≥0 a, f x < c
h✝ : Nontrivial A
hf : ContinuousOn f (σ ℝ≥0 a)
ha : 0 ≤ a
x : ℝ≥0
hx : x ∈ σ ℝ≥0 a
⊢ f x < c

Proof state:
case inr
A : Type u_1
inst✝⁶ : NormedRing A
inst✝⁵ : StarRing A
inst✝⁴ : NormedAlgebra ℝ A
inst✝³ : PartialOrder A
inst✝² : StarOrderedRing A
inst✝¹ : IsometricContinuousFunctionalCalculus ℝ A IsSelfAdjoint
inst✝ : NonnegSpectrumClass ℝ A
f : ℝ≥0 → ℝ≥0
a : A
c : ℝ≥0
hc : 0 < c
h : ∀ x ∈ σ ℝ≥0 a, f x < c
h✝ : Nontrivial A
hf : ContinuousOn f (σ ℝ≥0 a)
ha : 0 ≤ a
⊢ (fun x => ‖x‖₊ < c) ((cfcHom ha) { toFun := (σ ℝ≥0 a).restrict f, continuous_toFun := ⋯ })

Tactic:
simp only [← cfc_apply f a, (IsGreatest.nnnorm_cfc_nnreal f a hf ha |>.lt_iff)]

Result:
case inr
A : Type u_1
inst✝⁶ : NormedRing A
inst✝⁵ : StarRing A
inst✝⁴ : NormedAlgebra ℝ A
inst✝³ : PartialOrder A
inst✝² : StarOrderedRing A
inst✝¹ : IsometricContinuousFunctionalCalculus ℝ A IsSelfAdjoint
inst✝ : NonnegSpectrumClass ℝ A
f : ℝ≥0 → ℝ≥0
a : A
c : ℝ≥0
hc : 0 < c
h : ∀ x ∈ σ ℝ≥0 a, f x < c
h✝ : Nontrivial A
hf : ContinuousOn f (σ ℝ≥0 a)
ha : 0 ≤ a
⊢ ∀ x ∈ f '' σ ℝ≥0 a, x < c