src/Doc/Sledgehammer/document/root.tex

 \texttt{\$ISA\-BELLE\_\allowbreak HOME\_\allowbreak USER}, which is useful for
 debugging Sledgehammer but also unsafe if several instances of the tool are run
 simultaneously. The files are identified by the prefixes \texttt{prob\_} and
 \texttt{mash\_}; you may safely remove them after Sledgehammer has run.
 
+\textbf{Warning:} This option is not thread-safe. Use at your own risks.
+
 \nopagebreak
 {\small See also \textit{debug} (\S\ref{output-format}).}
 \end{enum}
 
 \subsection{Relevance Filter}