I know that the closed unit balls of center origion are convex sets in a normed space.
Can we say that open and closed balls are convex sets and speres are not cpnvex in normed spaces? (Here center may be any arbitrary point).
For example the below pictures is a ball in function space $C[a,b]$, so is it convex?
2026-04-24 02:19:02.1776997142
convex sets in normed spaces
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