English
If r > 0, then the center x belongs to the open ball of radius r around itself.
Русский
Если r > 0, то x принадлежит открытой сфере радиуса r вокруг x.
LaTeX
$$hr > 0 ⇒ x ∈ ball x r$$
Lean4
/-- If `E` is a finite-dimensional space over `ℝ`, then `toEuclidean` is a continuous `ℝ`-linear
equivalence between `E` and the Euclidean space of the same dimension. -/
def toEuclidean : E ≃L[ℝ] EuclideanSpace ℝ (Fin <| finrank ℝ E) :=
ContinuousLinearEquiv.ofFinrankEq finrank_euclideanSpace_fin.symm