C(12,6,2) = 6

Method of Construction: lex covering

 1  2  3  4  5  6 
 1  5  6  7  8 12 
 1  7  8  9 10 11 
 2  3  4  7  8 12 
 2  3  4  9 10 11 
 5  6  9 10 11 12