{ diff(x1, t) = (1*k14*k1*x5 + 1*k14*k2*k15 + (-1)*k14*k3*x1 + (-1)*k14*k4*x1*x2)/k14,
  diff(x2, t) = (1*k14*k9*x1 + (-1)*k14*k10*x2)/k14,
  diff(x3, t) = 0 }