On left democracy function

Abstract

We continue the study undertaken in \cite{GHN} of left democracy function $h_l(N)=\inf_{#Λ=N}\left\|\sum_{n\in Λ_N} x_n\right\| $ of an unconditional basis in a Banach space $X$. We provide an example of a basis with $h_l$ non-doubling. Then we show that for bases with non-doubling $h_l$ the greedy projection is not optimal. Together with results from \cite{GHN} and improved by C. Cabrelli, G. Garrigós, E. Hernandez and U. Molter we get that the basis is greedy if and only if the greedy projection is optimal.