C(13,6,2) <=7

Method of construction: lex covering

 1  2  3  4  5  6
 1  7  8  9 10 11
 2  3  7  8 12 13
 4  5  9 10 12 13
 2  3  6  9 10 11
 4  5  6  7  8 11
 1  2  6 11 12 13