“…We do not know how to prove this, but we have confirmed it numerically. More precisely, we conducted a numerical search based on the tabu-search algorithm (Harman et al, 2016;Jung and Yum, 1996) to find the D-optimal designs in D (n, m, b) for certain n, m and k. We used a modification of the R code of a tabusearch-based approach for chemical balance weighing designs by Katulska and Smaga (2016) (Domijan, 2012;R Core Team, 2015). It is significant that we did not find D-better designs than d 4 .…”