Circumference of a circle

[SnirBroshi]

For n : ℕ, define the n-dimensional sphere $S_n$ to be the set Metric.sphere (α := EuclideanSpace ℝ <| Fin <| n+1) 0 1.
Then the surface integral of 1 over $S_n$ equals $\frac{2\pi^{(n+1)/2}}{\Gamma((n+1)/2)}$

Wikipedia
Wikipedia

Zulip
Zulip

Try using MeasureTheory.Measure.euclideanHausdorffMeasure.