Let A be a family of proper closed subspaces of the Hilbert space H\equal{}l^2 totally ordered with respect to inclusion (that is
, if L1,L2∈A, then either L1⊂L2 or L2⊂L1). Prove that there exists a vector x∈H not contaied in any of the subspaces L belonging to A.
B. Szokefalvi Nagy vectorFunctional Analysisreal analysisreal analysis unsolved