English
The HasFPowerSeriesAt for all i implies HasFPowerSeriesAt for their pi-product.
Русский
HasFPowerSeriesAt для всех i подразумевает HasFPowerSeriesAt для их pi-произведения.
LaTeX
$$$HasFPowerSeriesAt (fun x \\mapsto (f i x)) (pi p) e \\Rightarrow (∀ i, HasFPowerSeriesAt (f i) (p i) e)$$$
Lean4
theorem pi (hf : ∀ i, HasFPowerSeriesAt (f i) (p i) e) :
HasFPowerSeriesAt (fun x ↦ (f · x)) (FormalMultilinearSeries.pi p) e :=
by
simp_rw [← hasFPowerSeriesWithinAt_univ] at hf ⊢
exact HasFPowerSeriesWithinAt.pi hf