fix equation

sheets/04_mip/dbst_mip/README.md

@@ -20,7 +20,7 @@ We are going with the second approach, because based on my experience, I expect
 For every undirected edge, $\{u,v\}\in E$ we introduce a boolean variable $x_{u,v} \in \mathbb{B}$ that is $1$ if we use the edge, and $0$ otherwise.
 
 The degree constraint of a maximal degree of $d$ can be expressed for every vertex $v\in V$ by
-\[\forall v\in V: \quad \sum\limits_{e \in \delta(\{v\})}x_e \leq d\]
+$$\forall v\in V: \quad \sum\limits_{e \in \delta(\{v\})}x_e \leq d$$
 
 Here, $\delta(S)$ defines for a set of vertices $S\subset V$ the edges with one end in $S$ and one end in $V\setminus S$, thus, the edges leaving $S$.