\begin{sequencediagram}
    \newthread{actor}{Actor}{}
    \newinst[3]{concordia}{:Concordia}{}
    \newinst[2]{eth}{:Ethereum}{}

    \begin{call}{actor}{Submit post vote}{concordia}{Updated topic page}

        \begin{call}{concordia}{Add post vote}{eth}{}
        \end{call}

    \end{call}
\end{sequencediagram}