{ x9 = x7*k16/(1 - k16)*(k4 + 1)/k4/(1 + k16/(1 - k16)*(k4 + 1)/k4),
  x10 = (k13 + 1)*(k14 - x3) - k13*x6,
  x11 = (k13 + 1)*x1 - k13*x13,
  x12 = (k13 + 1)*k15 - k13*x19,
  x14 = (k13 + 1)*x3 - k13*x8,
  x15 = x14 - 2*x11 - x16,
  x16 = (k13 + 1)*x2 - k13*x17,
  x18 = x19 - x17,
  x20 = x8 - 2*x13 - x17,
  x21 = x12 - x16,
  x23 = x5 + x7 + x24 + x26,
  x25 = x7*1/(1 + k16/(1 - k16)*(k4 + 1)/k4) }