x1, x2, x3, x4, x5, x6, x7, 
(x1*x2+x2*x3+x3*x4+x4*x5+x5*x6+x1)*x7-1
(x1*x3+x2*x4+x3*x5+x4*x6+x2)*x7-2
(x1*x4+x2*x5+x3*x6+x3)*x7-3
(x1*x5+x2*x6+x4)*x7-4
(x1*x6+x5)*x7-5
x6*x7-6
x1+x2+x3+x4+x5+x6+1
