The group by option offers another approach to solving divsion. To divide
the tabular variable T , whose heading is A1 · · ·AmB1 · · ·Bn by the tabular
variable S whose heading is B1 · · ·Bn we compute the number k of distinct
rows in S. Then, we seek to retrieve those m-tuples (a1, . . . , am) that occur in
T and are associated in that tabular variable with at least k distinct tuples.