    \documentclass{article}

    \usepackage{agda}

    \pagestyle{empty}

    \begin{document}

    \noindent Text.
    \AgdaHide{
    \begin{code}
      mutual
    \end{code}}
    \begin{code}
        postulate A : Set
    \end{code}
    More text.
    \begin{AgdaMultiCode}
    \begin{code}
      mutual
    \end{code}
    \begin{code}
        postulate B : Set
    \end{code}
    \end{AgdaMultiCode}
    Even more text.

    \end{document}