Non-linear approximation and interpolation spaces

We study n-term wavelet-type approximations in Besov and Triebel Lizorkin s paces. In particular, we characterize spaces of functions which have prescr ibed degree of n-term approximation in terms of interpolation spaces. These results are applied to identify interpolation spaces between Triebel Lizor kin and Besov spaces. (C) 2001 Academic Press.