let G be Go-board; :: thesis: Center G <= len G
A1: Center G = ((len G) div 2) + 1 by JORDAN1A:def 1;
0 < len G by GOBRD11:34;
then (len G) div 2 < len G by INT_1:83;
hence Center G <= len G by A1, NAT_1:13; :: thesis: verum