A series whose sum range is an arbitrary finite set


In finitely-dimensional spaces the sum range of a series has to be an affine subspace. It is long known this is not the case in infinitely dimensional Banach spaces. In particular in 1984 M.I. Kadets and K. Woz̀niakowski obtained an example of a series the sum range of which consisted of two points, and asked whether it is possible to obtain more than two… (More)