diff --git a/Robust-Graph-Optimization.md b/Robust-Graph-Optimization.md
index 1fac559..38e96de 100644
--- a/Robust-Graph-Optimization.md
+++ b/Robust-Graph-Optimization.md
@@ -58,4 +58,4 @@ An option can be also used with TORO (it works for the other algorithms too) to
 When large graph optimization errors are detected after a loop closure, this means that the last loop closure is a wrong loop closure. RTAB-Map can detect this with this parameter and remove the link from the graph directly. 
 
 ## Issues
- * The above example doesn't work when link covariances are Identity. There are some [cases](https://www.tu-chemnitz.de/etit/proaut/mitarbeiter/rsrc/IROS12-switchableConstraints.pdf) where Vertigo cannot correctly remove **all** wrong loop closures. Even one left can cause large errors in the map. With the combinaison of the parameter explained in the section [Without Vertigo](#without-vertigo), there is less chance that wrong loop closures are accepted. 
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+ * The above example doesn't work when link's covariances are Identity. There are some [cases](https://www.tu-chemnitz.de/etit/proaut/mitarbeiter/rsrc/IROS12-switchableConstraints.pdf) where Vertigo cannot correctly remove **all** wrong loop closures. Even one left can cause large errors in the map. With the combinaison of the parameter explained in the section [Without Vertigo](#without-vertigo), there is less chance that wrong loop closures are accepted. 
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