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