x1, x2, x3, x4, x5, x6, 
(x1*x2+x2*x3+x3*x4+x4*x5+x1)*x6-1
(x1*x3+x2*x4+x3*x5+x2)*x6-2
(x1*x4+x2*x5+x3)*x6-3
(x1*x5+x4)*x6-4
x5*x6-5
x1+x2+x3+x4+x5+1
