f✝ f : StieltjesFunction
⊢ {x | leftLim (↑f) x ≠ ↑f x} ⊆ {x | ¬ContinuousAt (↑f) x}
f✝ f : StieltjesFunction
⊢ Set.Countable {x | leftLim (↑f) x ≠ ↑f x}
refine Countable.mono ?_ f.mono.countable_not_continuousAt
f✝ f : StieltjesFunction
x : ℝ
hx : x ∈ {x | leftLim (↑f) x ≠ ↑f x}
h'x : ContinuousAt (↑f) x
⊢ False
f✝ f : StieltjesFunction
⊢ {x | leftLim (↑f) x ≠ ↑f x} ⊆ {x | ¬ContinuousAt (↑f) x}
intro x hx h'x
f✝ f : StieltjesFunction
x : ℝ
hx : x ∈ {x | leftLim (↑f) x ≠ ↑f x}
h'x : ContinuousAt (↑f) x
⊢ leftLim (↑f) x = ↑f x
f✝ f : StieltjesFunction
x : ℝ
hx : x ∈ {x | leftLim (↑f) x ≠ ↑f x}
h'x : ContinuousAt (↑f) x
⊢ False
apply hx
no goals
f✝ f : StieltjesFunction
x : ℝ
hx : x ∈ {x | leftLim (↑f) x ≠ ↑f x}
h'x : ContinuousAt (↑f) x
⊢ leftLim (↑f) x = ↑f x
exact tendsto_nhds_unique (f.mono.tendsto_leftLim x) (h'x.tendsto.mono_left nhdsWithin_le_nhds)