\item \self Given the formula $\phi$ with the variables $x_1, ..., x_n$. Tick all statements that are true. 
\begin{itemize}
	\item[$\square$] A \textit{literal} is a variables $x_i$ or its negation.
	\item[$\square$] A \textit{literal} forms a formula in conjunctive normal form.
	\item[$\square$] A \textit{literal} forms a formula in disjunctive normal form.	
	\item[$\square$] A \textit{literal} is called \textit{positive}, if it is the negation of a variable.
	\item[$\square$] A \textit{literal} is called \textit{negative}, if it is the negation of a variable.
\end{itemize}