a := (  1, 16,  2)(  3, 17, 30)(  4, 18, 31)(  5, 19, 32)(  6, 20, 33)
(  7, 21, 34)(  8, 22, 35)(  9, 23, 36)( 10, 24, 37)( 11, 25, 38)
( 12, 26, 39)( 13, 27, 40)( 14, 28, 41)( 15, 29, 42);