\item \ifassignmentsheet \points{3}
  \dpllDescriptionAssignmentSheet
\else \prac
  \dpllDescription{negative}
\fi
\begin{dpllCNFInput}
\item $\{a,\neg b, c \}$
\item $\{b,\neg c, d \}$
\item $\{a, \neg b \}$
\item $\{a ,c \}$
\item $\{\neg c, \neg d \}$
\item $\{\neg a, c \}$
\end{dpllCNFInput}