MAHAMAT YOUSSOUF, Ali Ahamad et al. The gravity model of international trade: the case of cotton initiative (WCA) countries. In ICABR 2013. 1. vyd. Online (635 s.). ISBN 978-0-620-55419-0. ICABR. Brno : Mendel University in Brno, 2013, s. 597-616, online. Dostupné na internete:<http://www.icabr.com/fullpapers/icabr2013.pdf> Indexované v: WoS