如何在对齐环境中实现两级缩进？

Question

我正在尝试将方程式进一步缩进 - 基本上是为了实现两级缩进。
让我再解释一下...

我有以下内容：

\documentclass{article}

\usepackage{parskip}
\usepackage{amssymb}
\usepackage[fleqn]{amsmath}


\begin{document}

        Suppose we want to compute $\nu(u_1)$, we first consider $Y_1$.\\ So $Y_1=A\setminus S_1=\{country, genre\}$, and we have that:\\
        \begin{align*}
        \nu(u_1)&=\exists(country, genre)(u\,'_1\wedge u\,'_2\wedge u\,'_3)\\
        &=\exists(country, genre)(\varphi\,'_1(cd, member, band)\wedge\\
        &\varphi\,'_2(cd,member, date)\wedge\\
        &\varphi\,'_3(cd, member,country))
        \end{align*}

        We now want to prove that similarity conditions hold for these three functions we defined.\\

\end{document}

由此产生了如下结果：

现在，我想要进一步缩进这个等式中的第三行和第四行，这样它们就会与对齐\varphi\,'_1。

我尝试采用建议的方法这里，并添加双 && 来增加缩进级别：

\documentclass{article}

\usepackage{parskip}
\usepackage{amssymb}
\usepackage[fleqn]{amsmath}


\begin{document}

        Suppose we want to compute $\nu(u_1)$, we first consider $Y_1$.\\ So $Y_1=A\setminus S_1=\{country, genre\}$, and we have that:\\
        \begin{align*}
        \nu(u_1)&=\exists(country, genre)(u\,'_1\wedge u\,'_2\wedge u\,'_3)\\
        &=\exists(country, genre)(&&\varphi\,'_1(cd, member, band)\wedge\\
        &   &&\varphi\,'_2(cd,member, date)\wedge\\
        &   &&\varphi\,'_3(cd, member,country))
        \end{align*}

        We now want to prove that similarity conditions hold for these three functions we defined.\\

\end{document}

但这产生了糟糕的输出：

虽然这三个\varphi现在对齐了，但它们不必要地被推到了右边，这显然不是我想要的……

我怎样才能正确实现第二级缩进？

任何帮助将不胜感激。

Answer 1

\documentclass{article}

\usepackage{parskip}
\usepackage{amssymb}
\usepackage[fleqn]{amsmath}


\begin{document}

        Suppose we want to compute $\nu(u_1)$, we first consider $Y_1$.\\ 
So $Y_1=A\setminus S_1=\{\mathit{country}, \mathit{genre}\}$, and we have that:\\
        \begin{align*}
        \nu(u_1)&=\exists(\mathit{country}, \mathit{genre})(u\,'_1\wedge u\,'_2\wedge u\,'_3)\\
        &=\exists(\mathit{country}, \mathit{genre})(
\!\begin{aligned}[t]
&\varphi\,'_1(\mathit{cd}, \mathit{member}, band)\wedge\\
&        \varphi\,'_2(\mathit{cd},\mathit{member}, date)\wedge\\
&        \varphi\,'_3(\mathit{cd}, \mathit{member},\mathit{country}))
\end{aligned}
        \end{align*}

        We now want to prove that similarity conditions hold for these 
three functions we defined.

\end{document}

您可以在内使用split或，但请注意，不要对多字母标识符使用数学斜体，并且不要用alignedalign\\

Answer 2

\varphi同样，只需制作以下行，即可从 OP 的第一个 MWE 获得结果\Longunderstack：

\documentclass{article}

\usepackage{parskip}
\usepackage{amssymb}
\usepackage[fleqn]{amsmath}
\usepackage[usestackEOL]{stackengine}
\stackMath
\begin{document}

        Suppose we want to compute $\nu(u_1)$, we first consider $Y_1$.\\ So $Y_1=A\setminus S_1=\{country, genre\}$, and we have that:\\
        \begin{align*}
        \nu(u_1)&=\exists(country, genre)(u\,'_1\wedge u\,'_2\wedge u\,'_3)\\
        &=\exists(country, genre)(\Longunderstack[l]{
          \varphi\,'_1(cd, member, band)\wedge\\
          \varphi\,'_2(cd,member, date)\wedge\\
          \varphi\,'_3(cd, member,country))
        }
        \end{align*}

        We now want to prove that similarity conditions hold for these three functions we defined.\\

\end{document}