C(7,4,3) = 12
Method of Construction: simple construction: combined c(v-1,k,t) and c(v-1,k-1,t-1)
Lower Bound: Handbook of Combinatorial Designs section on coverings
1 3 4 5
1 2 3 6
1 2 5 6
3 4 5 6
2 3 4 5
1 2 4 6
3 4 5 7
1 5 6 7
2 3 6 7
2 4 6 7
1 2 5 7
1 3 4 7