In the Amemiya-Ando problem 3 is enough
arXiv:1208.0905
Abstract
In any infinite dimensional Hilbert space there exist orthogonal projections , and , such that a sequence diverges in norm for some and .
arXiv:1208.0905
In any infinite dimensional Hilbert space there exist orthogonal projections , and , such that a sequence diverges in norm for some and .