[ Eq(Derivative(x1, t), ((-1)*k3*(k6 + k7*k1) + 1*k2*k14*x2)/k2),
  Eq(Derivative(x2, t), (1*k3*(k6 + k7*k1) + (-1)*k5*k8*x2**2/(k9**2 + x2**2) + 1*k3*k10*x3**2*x2**2/((k11**2 + x3**2)*(k12**2 + x2**2)) + 1*k3*k13*x3 + (-1)*k2*k14*x2 + 1*k3*k15*x4 + (-1)*k4*k16*x2**2/(k17**2 + x2**2) + 1*k3*k1*k18*x4**2/(k19**2 + x4**2))/k3),
  Eq(Derivative(x3, t), (1*k5*k8*x2**2/(k9**2 + x2**2) + (-1)*k3*k10*x3**2*x2**2/((k11**2 + x3**2)*(k12**2 + x2**2)) + (-1)*k3*k13*x3)/k5),
  Eq(Derivative(x4, t), ((-1)*k3*k15*x4 + 1*k4*k16*x2**2/(k17**2 + x2**2) + (-1)*k3*k1*k18*x4**2/(k19**2 + x4**2))/k4) ]