On the In-Out-Proper Orientations of Graphs

An orientation of a graph $G$ is {\it in-out-proper} if any two adjacent vertices have different in-out-degrees, where the in-out-degree of each vertex is equal to the in-degree minus the out-degree of that vertex. The {\it in-out-proper orientation number} of a graph $G$, denoted by $\overleftrightarrow{\chi }(G)$, is $ \min_{D\in \Gamma}\max_{v\in V(G)} |d_D^{\pm}(v)|$,where$\Gamma$isthesetofin-out-properorientationsof$G$and$d_D^{\pm}(v)$isthein-out-degreeofthevertex$v$intheorientation$D$.