\item \self  Given a propositional logic formula $\varphi$.
Tick all statements that are true. 
\begin{enumerate}
	\item[$\square$] A formula $\phi$ is \textit{valid}, if and only if $\lnot \phi$ is \textit{satisfiable}.
	\item[$\square$] A formula $\psi$ is \textit{satisfiable}, if and only if $\lnot \phi$ is \textit{valid}.
	\item[$\square$] A formula $\phi$ is \textit{satisfiable}, if and only if $\lnot \phi$ is \textit{not valid}.
	\item[$\square$] A formula $\phi$ is \textit{valid}, if and only if $\lnot \phi$ is \textit{not satisfiable}.
\end{enumerate}