“…(For simplicity, we just write the index i for variable X i .) The scope of C is the list of variables corresponding to the white boxes of the sequence D; the relation of C contains the legal words for D. For the example in Figure 1, we have C 1H = ((1, 2, 3, 4, 5), r 1H ), C 8H = ((8, 9, 10), r 8H ), C 11H = ( (11,12,13), r 11H ), C 20H = ( (20,21,22,23,24,25,26), r 20H ), C 1V = ( (1,7,11,16,20), r 1V ), C 5V = ( (5, 8, 14, 18, 24), r 5V ), C 6V = ((6, 10, 15, 19, 26), r 6V ), C 13V = ( (13,17,22), r 13V ). Subscripts H and V stand for "Horizontal" and "Vertical," respectively, resembling the usual naming of definitions in crossword puzzles.…”