{ diff(x1, t) = 0/k13,
  diff(x2, t) = ((-1)*k1*x1^3*k11^2*x18/((x18 + k11)*(x1^2*k11^2 + k10*x18^2 + 2*k10*k11*x18 + k10*k11^2))*x2*k13 + 1*k2*x7*k13)/k13,
  diff(x3, t) = (-1)*k3*x3*x7*k13/k13,
  diff(x4, t) = (-1)*k8*x4*(x10 + x11)*k13/k13,
  diff(x5, t) = (-1)*k9*x5*(x10 + x11)*k13/k13,
  diff(x6, t) = (-1)*k9*x6*x11*k13/k13,
  diff(x7, t) = (1*k1*x1^3*k11^2*x18/((x18 + k11)*(x1^2*k11^2 + k10*x18^2 + 2*k10*k11*x18 + k10*k11^2))*x2*k13 + (-1)*k2*x7*k13 + (-1)*k3*x3*x7*k13 + 1*k4*x10*k13 + 1*k5*x9*(x8 + x9)*k13 + 1*k6*x9*x10*k13)/k13,
  diff(x8, t) = (1*k3*x3*x7*k13 + (-1)*k4*x8*k13 + (-1)*k5*x8*(x8 + x9)*k13 + (-1)*k6*x8*x10*k13)/k13,
  diff(x9, t) = (1*k4*x8*k13 + (-1)*k5*x9*(x8 + x9)*k13 + (-1)*k6*x9*x10*k13)/k13,
  diff(x10, t) = ((-1)*k4*x10*k13 + 1*k5*x8*(x8 + x9)*k13 + 1*k6*x8*x10*k13)/k13,
  diff(x11, t) = (1*k4*x10*k13 + 1*k5*x9*(x8 + x9)*k13 + 1*k6*x9*x10*k13 + (-1)*k7*x11*k13)/k13,
  diff(x12, t) = 1*k7*x11*k13/k13,
  diff(x13, t) = 1*k8*x4*(x10 + x11)*k13/k13,
  diff(x14, t) = 1*k9*x5*(x10 + x11)*k13/k13,
  diff(x15, t) = 1*k9*x5*(x10 + x11)*k13/k13,
  diff(x16, t) = 1*k9*x6*x11*k13/k13,
  diff(x17, t) = 1*k9*x6*x11*k13/k13,
  diff(x18, t) = 0/k13 }