Consider the milk production data in Table 18.8 and the corresponding analysis of variance in Table 18.10. Relative to the periods, the squares on the left of Table 11.8 always have treatment A followed by B, B followed by C, and C followed by A. The squares on the right always have treatment A followed by C, B followed by A, and C followed by B. Test whether there is an average difference between the squares on the left and those on the right. Test whether there is an interaction between periods and left–right square differences.