在对齐环境中包括公式编号和注释

Question

我正在尝试编写连续证明，其中公式居中对齐，方程编号左对齐，注释右对齐。下面是我想要的示例：

但从我在 StackExchange 上看到的情况来看，对齐行上的标签会替换该行的编号，并共享相同的对齐设置。以下是我遇到的问题的一个示例。

\documentclass[leqno]{article}
\usepackage{amsmath}
\usepackage{amsthm}
\begin{document}
 \begin{align}
  Rab 
  &\implies Rab                                \tag{R0}
  \\ &\implies Rab,\neg Rab                    \tag{R2a}
  \\ &\implies Rab, \exists y \neg Ray   
  \\ \neg \exists y \neg Ray 
  &\implies Rab   
  \\ \forall y Ray 
  &\implies Rab      
  \\ \exists x \forall y Rxy 
  &\implies Rab   
  \\ \exists x \forall y Rxy 
  &\implies \exists x Rxb
  \\ \exists x \forall y Rxy, \neg \exists x Rxb 
  &\implies 
  \\ \exists x \forall y Rxy, \exists y \neg \exists x Rxy 
  &\implies 
  \\ \exists x \forall y Rxy 
  &\implies \neg \exists y \neg \exists x Rxy 
  \\ \exists x \forall y Rxy 
  &\implies \forall y \exists x Rxy \qedhere
 \end{align}
\end{document}

相应输出的图像：

Answer 1

只修改了前三行，但其余的应该很容易。唉，需要更多的 & 符号。

\documentclass[leqno]{article}
\usepackage{amsmath}
\usepackage{amsthm}
\begin{document}
 \begin{align}
  Rab 
  &\implies Rab                                &\text{(RO)}&
  \\ &\implies Rab,\neg Rab            &        \text{(R2aa)}&
  \\ &\implies Rab, \exists y \neg Ray  & \text{(and so on)}& 
  \\ \neg \exists y \neg Ray 
  &\implies Rab   
  \\ \forall y Ray 
  &\implies Rab      
  \\ \exists x \forall y Rxy 
  &\implies Rab   
  \\ \exists x \forall y Rxy 
  &\implies \exists x Rxb
  \\ \exists x \forall y Rxy, \neg \exists x Rxb 
  &\implies 
  \\ \exists x \forall y Rxy, \exists y \neg \exists x Rxy 
  &\implies 
  \\ \exists x \forall y Rxy 
  &\implies \neg \exists y \neg \exists x Rxy 
  \\ \exists x \forall y Rxy 
  &\implies \forall y \exists x Rxy \qedhere
 \end{align}
\end{document}

Answer 2

您可以通过以下环境轻松实现这一点flalign：

\documentclass[leqno]{article}
\usepackage{amsmath}
\usepackage{amsthm}

\begin{document}

 \begin{flalign}
  & & Rab &\implies Rab & \text{(R0)}
  \\ & & &\implies Rab,\neg Rab & \text{(R2a)}
  \\ & & &\implies Rab, \exists y \neg Ray
  \\ & & \neg \exists y \neg Ray &\implies Rab
  \\& & \forall y Ray &\implies Rab
  \\& & \exists x \forall y Rxy &\implies Rab
  \\ & & \exists x \forall y Rxy &\implies \exists x Rxb
  \\& & \exists x \forall y Rxy, \neg \exists x Rxb &\implies
  \\ & & \exists x \forall y Rxy, \exists y \neg \exists x Rxy &\implies
  \\ & & \exists x \forall y Rxy &\implies \neg \exists y \neg \exists x Rxy
  \\ & & \exists x \forall y Rxy &\implies \forall y \exists x Rxy \qedhere
 \end{flalign}

\end{document}