{ diff(x1, t) = ((-1)*k14*k4*(exp((-k13)*t)*k9 + (1 - exp((-k13)*t))*k11 + exp((-k13)*t)*k10 + (1 - exp((-k13)*t))*k12)/2*x1*x3/x5 + 1*k14*k2*x4)/k14,
  diff(x2, t) = (1*k14*k4*(exp((-k13)*t)*k9 + (1 - exp((-k13)*t))*k11 + exp((-k13)*t)*k10 + (1 - exp((-k13)*t))*k12)/2*x1*x3/x5 + (-1)*k14*k3*x2)/k14,
  diff(x3, t) = (1*k14*k3*x2 + (-1)*k14*k4*x3)/k14,
  diff(x4, t) = (1*k14*k4*x3 + (-1)*k14*k2*x4)/k14,
  diff(x5, t) = 0/k14 }