Eq. (1)
$$\sigma_{\rm BEB} = \frac{S}{t+(u+1)/n} \left[ \frac{Q \ln t}{2} \left( 1 - \frac{1}{t^2} \right) + (2-Q) \left( 1 - \frac{1}{t} - \frac{\ln t}{t+1} \right) \right]~ ,$$Eq. (2)
$Q = \frac{2}{N} \int \frac{B}{B+W} ~ \frac{{\rm d}f}{{\rm d}W} ~ {\rm d}W ~. $Eq. (3)
\begin{eqnarray*}\frac{{\rm d}\sigma(W,T)}{{\rm d}W}&=&\frac{S}{B[t+(u+1)/n]} \left\{ \frac{(N_i/N)-2}{t+1} \left( \frac{1}{w+1} + \frac{1}{t-w} \right) \right. \\ &+& \left. [2 - (N_i/N)] ~ \left[ \frac{1}{(w+1)^2} + \frac{1}{(t-w)^2} \right] + \frac{\ln t}{N(w+1)} ~ \frac{{\rm d}f(w)}{{\rm d}w} \right\} ~, \end{eqnarray*}Eq. (4)
${\rm d}f/{\rm d}w = ay^2 + by^3 + cy^4 + dy^5 + ey^6 ~ , $