[ Diff(x[1], t) = (1*k[1]*x[2] + (-1)*k[2]*x[1]*x[3])/k[15],
  Diff(x[2], t) = (1*k[13]*x[7] + (-1)*k[14]*x[2])/k[15],
  Diff(x[3], t) = (1*k[3]*x[4] + (-1)*k[4]*x[3])/k[15],
  Diff(x[4], t) = (1*k[9]*x[1] + (-1)*k[10]*x[6]*x[4])/k[15],
  Diff(x[5], t) = (1*k[5]*x[2] + (-1)*k[6]*x[3]*x[5])/k[15],
  Diff(x[6], t) = (1*k[7] + (-1)*k[8]*x[5]*x[6])/k[15],
  Diff(x[7], t) = (1*k[11]*x[1] + (-1)*k[12]*x[7])/k[15] ]