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\section{Pay}
\begin{figure}[h!]
\begin{sequencediagram}
\newinst{wallet}{\shortstack{Customer wallet \\
\\ \begin{tikzpicture}
\node [fill=gray!20,draw=black,thick,align=center] { Unique \\ Wallet ID};
\end{tikzpicture}
}}
\newinst[1]{merchant}{\shortstack{Merchant \\
\\ \begin{tikzpicture}[shape aspect=.5]
\tikzset{every node/.style={cylinder,shape border rotate=90, draw,fill=gray!25}}
\node at (1.5,0) {\shortstack{{{\tiny Database}}}};
\end{tikzpicture}
}}
\newinst[1]{exchange}{\shortstack{Taler (exchange) \\
\\ \begin{tikzpicture}[shape aspect=.5]
\tikzset{every node/.style={cylinder,shape border rotate=90, draw,fill=gray!25}}
\node at (1.5,0) {\shortstack{{{\tiny Database}}}};
\end{tikzpicture}
}}
\newinst[1]{bank}{\shortstack{Merchant bank \\
\\ \begin{tikzpicture}
\node [fill=gray!20,draw=black,thick,align=center] {Commercial \\ Accounts};
\end{tikzpicture}
}}
\postlevel
\mess[0]{wallet}{Browse catalog}{merchant}
\mess[0]{merchant}{Commercial offer}{wallet}
\begin{callself}{wallet}{Review offer}{}
\end{callself}
\mess[0]{wallet}{Send payment {(Coins)}}{merchant}
\mess[0]{merchant}{Deposit {(Coins)}}{exchange}
\begin{sdblock}{Acceptable account?}{}
\mess[0]{exchange}{{Refuse deposit}}{merchant}
\mess[0]{merchant}{{Refund purchase}}{wallet}
\end{sdblock}
\mess[0]{exchange}{{Confirm deposit}}{merchant}
\mess[0]{merchant}{Fulfill order}{wallet}
\begin{callself}{exchange}{Aggregate transactions}{}
\end{callself}
\begin{sdblock}{KYC/AML required?}{}
\begin{callself}{exchange}{Figures~\ref{fig:proc:kyc}, \ref{fig:proc:aml}}{}
\end{callself}
\end{sdblock}
\mess[0]{exchange}{{Initiate transfer}}{bank}
\end{sequencediagram}
\caption{Deposit interactions between customer, merchant,
Taler exchange (payment service provider) and merchant bank.}
\label{fig:int:pay}
\end{figure}
{\bf Internal note:} The exchange refusing a deposit immediately based on
unaccaptable merchant accounts may not be fully implemented (this is a very
recent feature, after all); especially the merchant then automatically
refunding the purchase to the customer is certainly missing. However,
the entire situation only arises when a merchant is incorrectly configured
and in violation of the terms of service.
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