[ Diff(x[1], t) = (1*x[5]*x[4] + (-1)*k[3]*x[1])/k[8],
  Diff(x[2], t) = (1*x[6]*x[4] + (-1)*k[4]*x[2])/k[9],
  Diff(x[3], t) = (1*k[3]*x[1] + 1*k[4]*x[2] + 1*k[10]*k[5] + (-1)*k[10]*k[6]*x[3])/k[10],
  Diff(x[4], t) = ((-1)*x[5]*x[4] + (-1)*x[6]*x[4])/k[7] ]