[ Eq(x1, k7 + Piecewise((k8, Le(t, k15)), (0, True)) + k9*t/k16),
  Eq(1*k17*x4 + 1*k17*x5 + 1*k17*x6 + 1*k17*x8, k17*k30),
  Eq(1*k17*x7 + 1*k17*x8 + 1*k17*x9, k17*k31) ]