[ Eq(x2, k2*x1/(k2 + k1)),
  Eq(x3, k1*x1/(k2 + k1)),
  Eq(x5, (1 + k8 + 2*k7*x4 - ((1 + k8 + 2*k7*x4)**2 - 8*k7*x4)**(1/2))/2),
  Eq(x7, (k10*x4 + k11*x6)/(1 + k10*x4 + k11*x6)*x17),
  Eq(x12, 1 - x11 - x13),
  Eq(x15, 1 - x14 - x16) ]