{ diff(x1, t) = ((-1)*k10*k3*x1 + 1*k10*(k2 - k1*x3)*(1 - piecewise(1, x3 - k2/k1 > 0, 0)))/k10,
  diff(x2, t) = (1*k10*k4*x1 + (-1)*k10*k5*x2)/k10,
  diff(x3, t) = (1*k10*k6*x2 + (-1)*k10*k7*x3)/k10 }