9 ≤ C(20,12,3) ≤ 10

Method of Construction: simple construction: multiple of smaller covering

Lower Bound: Schonheim

  1  2  3  4  5  6 11 12 13 14 15 16
  1  2  7  8  9 10 11 12 17 18 19 20
  3  4  5  7  8  9 13 14 15 17 18 19
  1  3  4  6  7 10 11 13 14 16 17 20
  2  5  6  8  9 10 12 15 16 18 19 20
  1  3  4  6  8  9 11 13 14 16 18 19
  2  3  4  8  9 10 12 13 14 18 19 20
  1  2  3  5  7 10 11 12 13 15 17 20
  1  5  6  7  8  9 11 15 16 17 18 19
  2  4  5  6  7 10 12 14 15 16 17 20