This question comes from this post.
This figure is trying to illustrate 4 spaces defined by 4 different set of standard basis.
In mathematics, the standard basis (also called natural basis) for a Euclidean space is the
set of unit vectors pointing in the direction of the axes of a Cartesian coordinate system.
if "set" is countable, the OP description would be 4 different sets of standard basis, so, is "set" here countable or not?