C(9,6,4) <=12

Method of construction: lex covering

 1  2  3  4  5  6
 1  2  3  7  8  9
 4  5  6  7  8  9
 1  2  4  5  7  8
 1  3  4  6  7  9
 2  3  5  6  8  9
 1  2  4  6  8  9
 1  3  5  6  7  8
 2  3  4  5  7  9
 1  2  5  6  7  9
 1  3  4  5  8  9
 2  3  4  6  7  8