PL

\begin{center}

$
P.L=
\begin{cases}

min \hspace{5pt} \sum\limits_{i=1}^{n} \sum\limits_{j=1}^{n} d_{i,j} x_{i,j},\\
\text{s.c.} \\

\hspace{30pt} \sum\limits_{i=1}^{n} x_{i,j}=1, \hspace{50pt} j=1,...,n, \hspace{150pt} (1.1)\\

\hspace{30pt} \sum\limits_{j=1}^{n} x_{i,j}=1, \hspace{50pt} i=1,...,n, \hspace{150pt} (1.2)\\

\hspace{30pt} \sum\limits_{i \in V} \sum\limits_{j \in V} x_{i,j} \leq  \lvert V \rvert -1 ,\hspace{10pt} V \subset \left \{ 1,...,n \right \},2\leq \lvert V \rvert \leq n-2,\hspace{35pt} (1.3) \\
\\

\hspace{30pt} x_{i,j} \in \left\{ 0,1 \right \}, \hspace{20pt} \forall (i,j) \in S^2.

\end{cases}
$

\end{center}