{ diff(x1, t) = 1*(k6*(1 - x1) + 2*(k4*x4 - k3*x3^2))/k46,
  diff(x4, t) = 1*(k3*x3^2 - (k4 + k5)*x4)/k46,
  diff(x6, t) = 1*k9*(x5 - x6)/k46,
  diff(x8, t) = 1*k12*((1 + k13)*x7 - (1 + k13*x7)*x8)/k46,
  diff(x9, t) = 1*k14*(x8 - x9/(1 + x11/k18 + x12/k24))/k46,
  diff(x10, t) = 1*k15*((1 + k16)*x6/(1 + k16*x6) - x10/(1 + x11/k20 + x12/k26))/k46,
  diff(x11, t) = 1*(k21*x12/(1 + x12/k22 + x13/k28) - k17*x9*x11/(1 + x11/k18 + x12/k24) - k19*x10*x11/(1 + x11/k20 + x12/k26))/k46,
  diff(x13, t) = 1*(k23*x9*x12/(1 + x11/k18 + x12/k24) + k25*x10*x12/(1 + x11/k20 + x12/k26) - k27*x13/((1 + x14/k30 + x15/k34)*(1 + x12/k22) + x13/k28))/k46,
  diff(x14, t) = 1*(k31*x19*x15/(1 + x15/k32 + x16/k36) - k29*x13*x14/(1 + x14/k30 + x15/k34))/k46,
  diff(x16, t) = 1*(k33*x13*x15/(1 + x14/k30 + x15/k34) - k35*x19*x16/(1 + x15/k32 + x16/k36))/k46,
  diff(x17, t) = 1*k37*((1 - x17)/k40 - x16^k39/(k38^k39 + x16^k39)*x17)/k46,
  diff(x18, t) = 1*k41*(x16 - x18)/k46,
  diff(x19, t) = 1*k42*(x18^k44/(k43^k44 + x18^k44) - (x19 - 1)/k45)/k46 }