[ Eq(x15, x1 + x4), Eq(1*k11*x1 + 1*k11*x2 + 1*k11*x3 + 1*k11*x4 + 1*k11*x5 + 1*k11*x6 + 1*k11*x7 + 1*k11*x8, k11*k18) ]