Szabó, Zoltán, and András Lőrincz. 2006. “ϵ-Sparse Representations : Generalized Sparse Approximation and the Equivalent Family of SVM Tasks”. Acta Cybernetica 17 (3):605-14. https://cyber.bibl.u-szeged.hu/index.php/actcybern/article/view/3685.