{ diff(x1, t) = 0/k13,
  diff(x2, t) = (1*k13*k1*x2*(1 - (x2 + x3)/k3) + (-1)*k13*(k4 + (1/2 + x1^2/(5^2 + x1^2))*k10/(k10 + x5^2))*x2)/k13,
  diff(x3, t) = (1*k13*k2*x3*(1 - (x2 + x3)/k3) + (-1)*k13*(k4 + k7*x4^2/(k8 + x4^2))*x3)/k13,
  diff(x4, t) = (1*k13*k5*x2 + (-1)*k13*(k11 + k4)*x4)/k13,
  diff(x5, t) = (1*k13*(1/50 + 3/100*x1^2/(5^2 + x1^2))*x3 + (-1)*k13*(k12 + k4)*x5)/k13,
  diff(x6, t) = 0,
  diff(x7, t) = 0 }