14 | | Actually, it is more than that. You can take the union of several families with the same `(G,k)` (the group `G` need to be fixed). If you have `(G,k,l1)`, `(G,k,l2)`, ..., `(G,k,ln)` difference families then you have a `(G,k,l1+l2+...+ln)` by taking the union. In other words, the set of `l` you can build for a fixed `(G,k)` is a semi-group of the integers... it is more than just stable under multiplicati~~ve~~. |

| 14 | Actually, it is more than that. You can take the union of several families with the same `(G,k)` (the group `G` need to be fixed). If you have `(G,k,l1)`, `(G,k,l2)`, ..., `(G,k,ln)` difference families then you have a `(G,k,l1+l2+...+ln)` by taking the union. In other words, the set of `l` you can build for a fixed `(G,k)` is a semi-group of the integers... it is more than just stable under multiplication. |