documentclass{book}
usepackage[font=small,format=plain,labelfont={bf,up},labelsep=space{caption}
usepackage{amsmath}
usepackage{mathtools}

begin{document}
begin{align*}
    verb|random| &= verb|variable|\
    & | verb|random : variable|\
    & | verb|<random> <variable>| end{align*}
end{document}