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(7,11).
next(11,12).
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(20,21).
next(18,22).
next(22,23).
next(23,24).
next(24,25).
next(22,26).
next(26,27).
next(27,28).
doAt(startflow,3).
doAt(a8,5).
doAt(a2,6).
doAt(a13,7).
doAt(a14,8).
doAt(endflow,9).
doAt(a1,11).
doAt(a10,12).
doAt(a6,13).
doAt(a3,14).
doAt(endflow,15).
doAt(a7,17).
doAt(a12,18).
doAt(a15,19).
doAt(endflow,20).
doAt(a9,22).
doAt(a11,23).
doAt(endflow,24).
doAt(a5,26).
doAt(endflow,27).
subsAt(a8,4).
leftrightnexts(23,26).
leftrightnexts(19,22).
leftrightnexts(14,17).
leftrightnexts(8,11).