$x_{ij}^k$	the decision variable that represents whether edge $(i,j)$ is used for the tour of $r_k$
	$x_{ij}^k=\left\{\begin{array}{cc}1\hfill & \mathrm{if}\mathrm{edge}(i,j)\mathrm{is}\mathrm{traveled}\mathrm{by}{r}_k\hfill \\ 0\hfill & \mathrm{otherwise}\hfill \end{array}\right.$
$z_U$	the decision variable that represents partition of targets in T
	$z_U=\left\{\begin{array}{cc}1\hfill & \mathrm{if}\mathrm{set}U\mathrm{contains}\mathrm{all}\mathrm{the}\mathrm{vertices}\mathrm{not}\mathrm{visited}\mathrm{by}{r}_1\hfill \\ 0\hfill & \mathrm{otherwise}\hfill \end{array}\right.$
t	the maximum travel cost