Explanation of terms used. For “Bordered Squares” the term Heart is given to the core around which the border is to be arranged. The Heart can be one of several different kinds. In our case, the rows and columns do not sum to the same amount; but the Heart is Associated, that is, every pair of numbers equidistant from the centre of the Heart in a straight line sums to the same amount, here 50. The numbers which make up such a pair are Complementary Numbers. When the numbers of these pairs are subtracted one from the other, they give the Complementary Differences.