doc-src/Sledgehammer/sledgehammer.tex

 environment variable \texttt{SPASS\_HOME} to the directory that contains the
 \texttt{SPASS} executable, or install the prebuilt SPASS package from Isabelle's
 download page. Sledgehammer requires version 3.5 or above. See
 \S\ref{installation} for details.
 
-\item[$\bullet$] \textbf{\textit{spass\_dfg}:} Same as the above, except that
-Sledgehammer communicates with SPASS using the native DFG syntax rather than the
-TPTP syntax. Sledgehammer requires version 3.0 or above. This ATP is provided
-for compatibility reasons.
-
 \item[$\bullet$] \textbf{\textit{vampire}:} Vampire is an ATP developed by
 Andrei Voronkov and his colleagues \cite{riazanov-voronkov-2002}. To use
 Vampire, set the environment variable \texttt{VAMPIRE\_HOME} to the directory
 that contains the \texttt{vampire} executable.