latex 在多行公式环境中添加右对齐文字标签 / align, equations, \tag

没有符号，默认是文字格式
\tag*{}
有数学符号就加入行内环境
https://tex.stackexchange.com/questions/356132/tagging-equations-with-different-symbols
\tag*{$\alpha$}

序列条件熵递减

\[\begin{align*} H(X_{n}|X^{n-1}) &\leq H(X_{n}|X_{2},\cdots,X_{n-1}) \tag*{remove $X_{1}$} \\ &\leq H(X_{n-1}|X^{n-2}) \tag*{stationarity} \\ &\leq H(X_{i}|X^{i-1}) \tag*{for every i} \end{align*}\]