{ x6 = k13 - x5,
  x8 = x7 - x11,
  x10 = x9 - x11,
  x16 = x14 - x15,
  x18 = k42 - x17,
  x20 = k50 - x19,
  x22 = (1 + k51*k52*x10)/(1 + k52*x10)*k53,
  x23 = k28 - x12 - x13,
  x24 = k29 - x13 }