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