diff --git a/Data/Graph/Libgraph.hs b/Data/Graph/Libgraph.hs
--- a/Data/Graph/Libgraph.hs
+++ b/Data/Graph/Libgraph.hs
@@ -30,6 +30,7 @@
 , display
 , collapse
 , remove
+, treeDepth
 ) where
 import Data.Graph.Libgraph.Core
 import Data.Graph.Libgraph.DepthFirst
diff --git a/Data/Graph/Libgraph/Core.hs b/Data/Graph/Libgraph/Core.hs
--- a/Data/Graph/Libgraph/Core.hs
+++ b/Data/Graph/Libgraph/Core.hs
@@ -1,7 +1,8 @@
 module Data.Graph.Libgraph.Core where
 import Data.Maybe
 import Data.List
-import Debug.Trace(traceStack)
+import Data.Map.Strict(Map)
+import qualified Data.Map.Strict as Map
 
 --------------------------------------------------------------------------------
 -- External representation of graphs
@@ -46,6 +47,18 @@
 succs :: Eq vertex => Graph vertex arc -> vertex -> [vertex]
 succs g v = map target $ filter ((== v) . source) (arcs g)
 
+
+succCache :: Ord vertex => Graph vertex arc -> (vertex -> [vertex])
+succCache g = \v -> case Map.lookup v m of 
+                        Nothing -> []
+                        (Just ws) -> ws
+
+  where m = foldl (\m' (Arc v w _) -> insertCon v w m') Map.empty (arcs g)
+  
+
+insertCon :: Ord k => k -> a -> Map k [a] -> Map k [a]
+insertCon i x = Map.insertWith (\[x] xs->x:xs) i [x]
+
 -- | Direct predecessors of a vertex.
 preds :: Eq vertex => Graph vertex arc -> vertex -> [vertex]
 preds g v = map source $ filter ((== v) . target) (arcs g)
@@ -102,3 +115,16 @@
 
 fstList :: [(a,b)] -> [a]
 fstList = fst . unzip
+
+---
+
+treeDepth :: Ord v => Graph v a -> Int
+treeDepth g = treeDepth' [] (root g)
+  where suc = succCache g
+
+        treeDepth' seen v
+          | v `elem` seen = 1
+          | otherwise     = case suc v of
+             [] -> 0
+             cs -> 1 + (maximum . map (treeDepth' (v:seen)) $ cs)
+
diff --git a/Data/Graph/Libgraph/Dot.hs b/Data/Graph/Libgraph/Dot.hs
--- a/Data/Graph/Libgraph/Dot.hs
+++ b/Data/Graph/Libgraph/Dot.hs
@@ -26,7 +26,8 @@
 showVertex :: (vertex->(String,String)) -> (vertex,Int) -> String
 showVertex vLabel (v,i) =
   let (lbl,extra) = vLabel v
-  in  vName i ++ " [label=\"" ++ escape lbl ++ "\"" ++ extra ++ "]\n"
+  in  vName i ++ " [label=" ++ lbl ++ "" ++ extra ++ "]\n"
+  -- in  vName i ++ " [label=\"" ++ escape lbl ++ "\"" ++ extra ++ "]\n"
 
 showArc :: Eq vertex => [(vertex,Int)] -> (Arc vertex arc->String) -> (Arc vertex arc) -> String
 showArc vs aLabel a
diff --git a/libgraph.cabal b/libgraph.cabal
--- a/libgraph.cabal
+++ b/libgraph.cabal
@@ -1,5 +1,5 @@
 Name:           libgraph
-Version:        1.4
+Version:        1.5
 Homepage:      http://maartenfaddegon.nl
 Synopsis:       Store and manipulate data in a graph.
 Description:    A graph type, analysis of graphs and manipulation of graphs.
@@ -25,7 +25,7 @@
                      Data.Graph.Libgraph.Dagify
                      Data.Graph.Libgraph.AlgoDebug
   default-language:  Haskell2010
-  ghc-prof-options:  -auto-all
+-- ghc-prof-options:  -auto-all
 
 -- Executable Libgraph-test
 --   Build-Depends:     base >= 4 && < 5, monads-tf, process