English
If HasFPowerSeriesAt f p x and f approximates g at x in nhds, then HasFPowerSeriesAt g p x.
Русский
Если у HasFPowerSeriesAt f p x и f сходится с g в окрестности x, тогда HasFPowerSeriesAt g p x.
LaTeX
$$$HasFPowerSeriesAt\ f p x \Rightarrow (nhds(x)).EventuallyEq f g \Rightarrow HasFPowerSeriesAt\ g p x$$$
Lean4
theorem unique (hf : HasFPowerSeriesWithinOnBall f p s x r) (hg : HasFPowerSeriesWithinOnBall g p s x r) :
(insert x s ∩ EMetric.ball x r).EqOn f g := fun _ hy ↦ (hf.hasSum_sub hy).unique (hg.hasSum_sub hy)