Olga Holtz Amos Ron Approximation orders of shift-invariant subspaces of W<sup>s</sup><sub>2</sub>(R<sup>d</sup>). 97-148 2005 132 Journal of Approximation Theory 1 http://dx.doi.org/10.1016/j.jat.2004.10.006 db/journals/jat/jat132.html#HoltzR05