next(1,2).
next(2,3).
next(3,4).
next(4,5).
next(5,6).
next(6,7).
next(7,8).
next(8,9).
next(9,10).
next(10,11).
next(8,12).
next(12,13).
next(13,14).
next(14,15).
next(15,16).
next(13,17).
next(17,18).
next(18,19).
next(19,20).
next(17,21).
next(21,22).
next(22,23).
next(23,24).
next(24,25).
next(25,26).
next(26,27).
doAt(startflow,4).
doAt(a5,5).
doAt(a13,7).
doAt(a8,8).
doAt(a12,9).
doAt(endflow,10).
doAt(a3,12).
doAt(a14,13).
doAt(a15,14).
doAt(endflow,15).
doAt(a2,17).
doAt(a9,18).
doAt(endflow,19).
doAt(a11,21).
doAt(a7,22).
doAt(a4,23).
doAt(a6,24).
doAt(a1,25).
doAt(endflow,26).
subsAt(a13,6).
leftrightnexts(18,21).
leftrightnexts(14,17).
leftrightnexts(9,12).