在第二个等号处对齐，不添加空格

Question

我有以下输出：

生成上述图像的代码如下所示。我想要删除第一行中的这个多余空格，有什么想法吗？

  \begin{align*}
    \alpha \fatsemi (\beta \fatsemi \gamma) &\iff 
    \forall c \in \mathcal C, &\alpha_c \fatsemi (\beta \fatsemi \gamma)_c &=
    \alpha_c \fatsemi (\beta_c \fatsemi \gamma_c)\\& &&=
    (\alpha_c \fatsemi \beta_c) \fatsemi \gamma_c \\& &&= 
    (\alpha_c \fatsemi \beta_c) \fatsemi \gamma_c \\& &&= 
    (\alpha \fatsemi \beta)_c \fatsemi \gamma_c \\
                                            &\iff
    (\alpha \fatsemi \beta) \fatsemi \gamma
  \end{align*}

Answer 1

你想筑巢aligned。

\documentclass{article}
\usepackage{amsmath}
\usepackage{stmaryrd}

\begin{document}

\begin{align*}
\alpha \fatsemi (\beta \fatsemi \gamma)
&\iff 
  \begin{aligned}[t]
  \forall c \in \mathcal C,\ 
  \alpha_c \fatsemi (\beta \fatsemi \gamma)_c
  &=\alpha_c \fatsemi (\beta_c \fatsemi \gamma_c)\\
  &=(\alpha_c \fatsemi \beta_c) \fatsemi \gamma_c \\
  &=(\alpha_c \fatsemi \beta_c) \fatsemi \gamma_c \\
  &=(\alpha \fatsemi \beta)_c \fatsemi \gamma_c
  \end{aligned} \\
&\iff (\alpha \fatsemi \beta) \fatsemi \gamma
\end{align*}

\end{document}

barbara beeton 在评论中让我注意到你有一个 QED 标记，所以我假设显示结束了一个证明。在这种情况下，你需要\qedhere。

\documentclass{article}
\usepackage{amsmath}
\usepackage{amsthm}
\usepackage{stmaryrd}

\begin{document}

\begin{proof}
Some words to start the proof
\begin{align*}
\alpha \fatsemi (\beta \fatsemi \gamma)
&\iff 
  \begin{aligned}[t]
  \forall c \in \mathcal C,\ 
  \alpha_c \fatsemi (\beta \fatsemi \gamma)_c
  &=\alpha_c \fatsemi (\beta_c \fatsemi \gamma_c)\\
  &=(\alpha_c \fatsemi \beta_c) \fatsemi \gamma_c \\
  &=(\alpha_c \fatsemi \beta_c) \fatsemi \gamma_c \\
  &=(\alpha \fatsemi \beta)_c \fatsemi \gamma_c
  \end{aligned} \\
&\iff (\alpha \fatsemi \beta) \fatsemi \gamma
\qedhere
\end{align*}
\end{proof}

\end{document}