example: cycle graph C_{N}
add sat_count/2 for testing

For example, the cycle graph C_100 has 1630580875002 kernels:

   %?- kernel(_,_,Sat), clpb:sat_count(Sat, C).
   %@ Sat = ~ (... + ... + ... * ... + _G117*_G118+_G118*_G117+_G118*_G119+_G119*_G118+_G20*_G119+_G119*_G20)* (... * ... * (... + ...)* (_G113+ (... + ...))* (_G114+ (... + ... + _G115))* (_G115+ (0+_G114+_G116))* (_G116+ (0+_G115+_G117))* (_G117+ (0+_G116+_G118))* (_G118+ (0+_G117+_G119))* (_G119+ (0+_G20+_G118))),
   %@ C = 1630580875002.