How to define an "align" environment with typewriter font?

Question

I tried to use the commands defined here: Can I change all math output to use monospaced text? to change the font in the math environment. However, the following code does not compile:

\everymath{\mathtt{\xdef\tmp{\fam\the\fam\relax}\aftergroup\tmp}}
\everydisplay{\mathtt{\xdef\tmp{\fam\the\fam\relax}\aftergroup\tmp}}
    \begin{align*}
        T = \{
              \alpha : A \subseteq B,\\
               \beta : B \subseteq C\\
            \}
    \end{align*}

It compiles correctly in normal math mode (without using "align" and line breaks), or without the commands to change the font. How can I modify the font used inside the align environment to typewriter? (Similar to: \newenvironment where all text is typewriter (like \texttt) , but in math mode)

I would like to write something like:

    \begin{ttalign*}
        T = \{
              \alpha : A \subseteq B,\\
               \beta : B \subseteq C\\
            \}
    \end{ttalign*}

where the environment "ttalign" behaves likes "align", but with the typewriter font instead of the normal font.

Answer 1

You don't need to reset \tmp every time: when you use \mathtt once, the relative math group is allocated and will no longer change.

\documentclass{article}
\usepackage{amsmath}

\newenvironment{ttmath}
 {\everymath{\ttmathgroup}\everydisplay{\ttmathgroup}}
 {}

\AtBeginDocument{%
  $\mathtt{\xdef\ttmathgroup{\fam\the\fam\relax}}$%
}

\begin{document}

\begin{align*}
T = \{
      &\alpha : A \subseteq B,\\
      &\beta : B \subseteq C\\
    \}
\end{align*}

\begin{ttmath}
\begin{align*}
T = \{
      &\alpha : A \subseteq B,\\
      &\beta : B \subseteq C\\
    \}
\end{align*}
\end{ttmath}

\end{document}

You can define a ttalign* environment, if you prefer:

\newenvironment{ttalign*}
 {\everymath{\ttmathgroup}\everydisplay{\ttmathgroup}\csname align*\endcsname}
 {\endalign}

Answer 2

Since I was already using xparse, I defined a new environment this way:

\NewDocumentEnvironment{ttmath}{}{\begingroup\everymath{\mathtt{\xdef\tmp{\fam\the\fam\relax}\aftergroup\tmp}}}{\endgroup}

And then, combined with the original align environment:

\begin{ttmath}
  \begin{align*}
        T = \{
            &\alpha : A \subseteq B,\\
            &\beta : B \subseteq C\\
        \}
    \end{align*}
\end{ttmath}