diff --git a/main/background.tex b/main/background.tex
index 793bf00..f58b76a 100644
--- a/main/background.tex
+++ b/main/background.tex
@@ -133,7 +133,7 @@ where $Q$ is the matrix of transition probabilities between
   \label{definitionN}
   \end{equation}
   where $I_{n-1}$ is the $(n-1)\times(n-1)$ identity matrix.
-  $N$ is a reachability matrix. 
+  $N$ is a transitive closure, and a reachability relation. 
   From state $i$, it is possible to reach state $j$ in an 
   expected number of steps $N_{ij}$.
  $N_{ij}=0$ means that state $i$ is not reachable to state $j$.