\begin{align}
    \mathcal{L}_{cls} &= -\alpha^t_i (1-p^t_i)^{\gamma^{\prime}} \log(p^t_i)\\
    p^{t}_i &=
    \begin{cases}
      p^s_i & \text{if $l_i$ = 1}\\
      1-p^s_i & \text{otherwise}\\
    \end{cases}\\
    \alpha^{t}_i &=
    \begin{cases}
      \alpha^t & \text{if $l_i$ = 1}\\
      1-\alpha^t_i & \text{otherwise}
    \end{cases}
\end{align}
