TeX source:

\sum_{j} X_{k, r, i, j}-\sum_{j} X_{k, r, i, j}=\left\{\begin{array}{ll}-1, & i=o ; \\1, & i=d ; \\0, & \text { otherwi7D\end{array} \quad \forall i \in N, \forall k \in K, \forall r \in R\right.