[ Eq(1/16*k1*x1 + 1/4*k2*x2 + 1/4*k3*x3 + 1/16*k1*x4, k1*k15 + k2*k16 + k3*k17),
  Eq(1*k1*x4 + 1*k1*x5, k1*k18) ]