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