\documentclass{article}
\input{6824-preamble}

\begin{document}
\psetnum{13}
\date{2005/04/14}

\begin{pset}
  Suppose $R_1$ has deleted file $F$ and thrown away the deletion
  notice. If this is true, it must be because the directory containing
  $F$ was synchronized, and thus a bound on the deletion time can be
  obtained from the synchronization time of the directory. If $R_2$
  then modifies $F$, during synchronization the two replicas will
  discover that a conflict exists because $F$ was modified on both
  copies since $R_2$'s last synchronization time. 
\end{pset}

\end{document}