答案1
根据您的对齐要求,可以执行以下操作:
\documentclass{article}
\usepackage{amsmath}
\begin{document}
\begin{subequations}
\begin{align}
\forall l \in L, & \quad a = 1 \\
\forall l \in L, & \quad b = 2 \\
\forall l \in L, & \quad c
\end{align}
\end{subequations}
\begin{subequations}
\begin{align}
&{\left.\kern-\nulldelimiterspace
\renewcommand{\arraystretch}{1.5}
\setlength{\arraycolsep}{0pt}
\begin{array}{l}
\forall l \in L, \quad a = 1 \\
\forall l \in L, \quad b = 2
\end{array}
\right\}} \\
&\forall l \in L, \quad c
\end{align}
\end{subequations}
\end{document}