خلفبتول, حاتماوس, and محمدمحمد. “Apply Six Sigma in Improving the Quality of Projects Added Expert System )Applied Research(”. Journal of Economics and Administrative Sciences 25, no. 114 (October 1, 2019): 168-193. Accessed December 4, 2019. http://jeasiq.uobaghdad.edu.iq/index.php/JEASIQ/article/view/1727.