[ Eq(Derivative(x3, t), (1*k15*1/(1 + (k8/x3)**k10)*k4*x3*(log(k9, 10) - log(x3, 10))/log(k9, 10) + (-1)*k15*k5*x1*x3/(k11 + x1 + x3))/k15),
  Eq(Derivative(x1, t), Piecewise((k1*x1*x3/(k3 + x1 + x3), Le(t, k12)), ((-(k6 + k2))*x1, True))),
  Eq(Derivative(x2, t), Piecewise((0, Le(t, k12)), (k6*x1 - k7*x2, True))) ]