\begin{equation}
\begin{aligned}
R(S_2)&= p_2\cdot S_2=\sum_{i\in \mathcal{I}^+(p_2)}B_i+\beta B_{l'}\\
&\leq \sum_{i\in \mathcal{I}^+(p_2)}B_i+B_{l'}\leq \sum_{i\in \mathcal{I}^+(p_1)}B_i \\
&\leq \sum_{i\in \mathcal{I}^+(p_1)}B_i+\alpha B_l=R(S_1)
\end{aligned}
\end{equation}

 

其中，\\ 表示换行， & 表示对齐点