# Tag Info

Introduce a binary variable $\delta \in \{0,1\}$ to indicate whether $q$ is positive or not. You want: $$\sum_{(i,j) \in A}f_{ij} \le |A| - 1 \quad \Longrightarrow \quad \delta=0$$ or the contrapositive: $$\delta=1 \quad \Longrightarrow \quad \sum_{(i,j) \in A}f_{ij} \ge |A|$$ which you can achieve with: $$\sum_{(i,j) \in A}f_{ij} \ge |A| \delta$$ ...