Lebesgue type inequalities for quasi-greedy bases
  We show that for quasi-greedy bases in real or complex Banach spaces the error of the thresholding greedy algorithm of order N is bounded by the best N- term error of approximation times a function of N which depends on the democracy functions and the quasi-greedy constant of the basis. If the basis is democratic this function is bounded by C logN. We show with two examples that this bound is attained for quasi-greedy democratic bases. 
Gustavo Garrig\'os, Eugenio Hern\'andez, Timur Oikhberg
math.FA