Design Theory: Antiquity to 1950

For j ∈ {0, 1, 2} let Qj = {{(i + 3, j), (i+ 5, j + 2), (i+ 6, j + 1)} : i = 0, . . . , 6}. The 70 sets in B are partitioned into ten classes (P0,P1, . . . ,P6,Q1,Q2,Q3) of seven sets each in this manner.