Can a set of numbers (not tuples) be called a convex set?
I have read this article:
where at the beginning is written an underlined text, saying that "where the domain of $f$ is a convex set" ("convex set" there is underlined). Function $f$ is one variable function.
My idea of a convex set is a $2D$ or $3D$ shape where every point on a line segment $AB,$ where points $A,B$ belong to the set, also belongs to the set.