[ Eq(Derivative(x1, t), 0),
  Eq(Derivative(x2, t), (1*k1*k14*k2*k12/k3/(1 + k12/k3 + x2/k4)/(1 + k13/k5) + (-1)*k1*k15*k6*x2/k7/(1 + x2/k7 + x3/k8))/k1),
  Eq(Derivative(x3, t), (1*k1*k15*k6*x2/k7/(1 + x2/k7 + x3/k8) + (-1)*k1*k16*k9*x3/k10/(1 + x3/k10 + k13/k11))/k1),
  Eq(Derivative(x4, t), 0),
  Eq(Derivative(x5, t), 0),
  Eq(Derivative(x6, t), 0),
  Eq(Derivative(x7, t), 0) ]