Use NewIntMap InvInt for crInv

src/Dodge/DoubleTree.hs

@@ -165,6 +165,7 @@ dtToUpDownAdj f (DT x l r) =
 
 -- returns an adjacency map with oldest ancestor and direct parent if they exist
 -- and any left and right children
+-- this should be all involving invids
 dtToLRAdj :: (a -> Int) -> DTree a -> IM.IntMap (Maybe (Int, Int), [Int], [Int])
 dtToLRAdj f (DT x l r) =
     IM.insert i (Nothing, map g l, map g r)