Elisabetta Alvoni Fabrizio Durante Pier Luigi Papini Carlo Sempi Different Types of Convexity and Concavity for Copulas. 185-189 2007 EUSFLAT Conf. (1) http://www.eusflat.org/publications/proceedings/EUSFLAT_2007/papers/Sempi_Carlo_(119).pdf conf/eusflat/2007-1 db/conf/eusflat/eusflat2007-1.html#AlvoniDPS07