Question

Prove that every open sphere is an open set in a metric space.​

Answer 1

Step-by-step explanation:

A set A ⊆ X is open if it contains an open ball about each of its points. ... An open ball in a metric space (X, ϱ) is an open set. Proof. If x ∈ Br(α) then ϱ(x, α) = r − ε where ε > 0.