C(9,7,4) = 6
Method of Construction: lex covering
Lower Bound: Schonheim
1 2 3 4 5 6 7 1 2 3 4 5 8 9 1 2 3 6 7 8 9 1 4 5 6 7 8 9 2 3 4 5 6 7 8 2 3 4 5 6 7 9