lower bound = 6

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