Alignment and dotfill in cases

Question

This is what I want: This is what I get:

I want two (or three) equations in cases and I want to align the equal sign (that's no problem). And then I want to have some text in every row. The text should be right aligned and I want dots between the equation and the text, just like it is when I don't have cases. I don't know how to right align the texts inside the cases. Here is my code:

\documentclass[a5paper]{book}

    \usepackage[top=1.8cm, bottom=2.7cm, left=2.7cm, right=1.8cm]{geometry}

    \usepackage{amsthm,amsmath}

    \makeatletter
    \renewcommand \dotfill {\leavevmode \cleaders \hb@xt@ .33em{\hss .\hss }\hfill \kern \z@}
    \makeatother

    \newenvironment{lcases}
    {\left\lbrace\begin{aligned}}
        {\end{aligned}\right.}

    \begin{document}    
        \begin{enumerate}
            \item $AB=CD$ \dotfill text
            \item $AB=CD$ \dotfill more text
            \item $\begin{lcases}
            &GB=DE \leaders\hbox{\hss .\hss }\hskip \textwidth minus \textwidth \text{text}\\
            &AB=CD \leaders\hbox{\hss .\hss }\hskip \textwidth minus \textwidth \text{more text}
            \end{lcases}$
        \end{enumerate}         
    \end{document}

Answer 1

This is not what you want. I don't understand why in each line of cases, you use some text at the end of line. If so, you can use, for example $AB=CD$ \dotfill 1 point without using cases. In my answer, in the cases, I also use \dotfill for all lines.

\documentclass[a5paper]{book}
  \usepackage[top=1.8cm, bottom=2.7cm, left=2.7cm, right=1.8cm]{geometry}
\usepackage{amsthm,amsmath}
  \begin{document}
        \begin{enumerate}
            \item $AB=CD$ \dotfill 1 point
            \item $AB=CD$ \dotfill 2 points
            \item $\begin{cases}
                 GB=DE\\
                 AB=CD.                 
                 \end{cases}$ \dotfill 2 points
        \end{enumerate} 
    \end{document}

Answer 2

An easy way to obtain the desired result, namely

is to use the tabularx environment (requires the tabularx package). Indeed, the above printout has been produced with the following code:

% My standard header for TeX.SX answers:
\documentclass[a4paper]{article} % To avoid confusion, let us explicitly 
                                 % declare the paper format.

\usepackage[T1]{fontenc}         % Not always necessary, but recommended.
% End of standard header.  What follows pertains to the problem at hand.

\usepackage{amsmath}
\usepackage{tabularx}

\makeatletter

\newcommand*\Annadotfill{%
    \leavevmode
    % Do you really want "\cleaders"?
    \cleaders \hb@xt@ .33em{\hss .\hss }\hfill
    \kern \z@
}
\@ifdefinable\@Anna@brace@width{\newdimen\@Anna@brace@width}
\settowidth\@Anna@brace@width{%
    $\left\{\vbox{\vskip \@m \p@}\right.\kern -\nulldelimiterspace$%
}
\newenvironment{Annacases}{%
    \left\{%
    \tabcolsep \z@
    \def\arraystretch{1.2}% linespread: adjust as you please
    \tabularx{\dimexpr \linewidth-\@Anna@brace@width \relax}%
                {>{$}r<{$}>{${}}X<{$}}%
}{%
    \endtabularx
    \right.%
    \kern -\nulldelimiterspace
}

\makeatother



\begin{document}

Some text before the enumeration.
\begin{enumerate}
    \item $AB=CD$ \Annadotfill text;
    \item $AB=CD$ \Annadotfill longer text;
    \item
        $
            \begin{Annacases}
                AB &= CD\Annadotfill\text{text;}\\
                AB &= CD+EF+GH\Annadotfill\text{longer text;}\\
                MN+XY &= PQ\Annadotfill\text{longer text, and more.}
            \end{Annacases}
        $
\end{enumerate}
Some text after the enumeration.

\end{document}

However, there must be a more efficient method, using primitive TeX commands…

---

Previous Attempt, Which I Had Deleted

Something like this?

This is the code:

% My standard header for TeX.SX answers:
\documentclass[a4paper]{article} % To avoid confusion, let us explicitly 
                                 % declare the paper format.

\usepackage[T1]{fontenc}         % Not always necessary, but recommended.
% End of standard header.  What follows pertains to the problem at hand.

\usepackage{mathtools} % also loads "amsmath"

\makeatletter

\newcommand*\annadotsfill{\leaders\hbox{.\,}\hskip 2em \@plus 1fill \relax}
\newcases{annacases}
    {} % separation between columns
    {$\m@th\displaystyle\hfil##$} % left preamble
    {$\m@th\displaystyle{}##$} % right preambel
    {\lbrace}{.} % delimiters

\makeatother



\begin{document}

Some text before the equation.
\[
    \begin{annacases}
        AB &= CD\annadotsfill\text{text}\\
        AB &= CD+EF+GH\annadotsfill\text{longer text}\\
        MN+XY &= PQ\annadotsfill\text{longer text, and more}
    \end{annacases}
\]
Some text after the equation.

\end{document}

Unfortunately, I cannot dwell on explanations right now; I’ll try to edit this answer later on.