C(15,13,2) <=3

Method of construction: lex covering

 1  2  3  4  5  6  7  8  9 10 11 12 13
 1  2  3  4  5  6  7  8  9 10 11 14 15
 1  2  3  4  5  6  7  8  9 12 13 14 15