Bertram, Christian, thank you for help. Can somebody apply the patch posted by Bertram in the previous message? Please let me know if it is better to submit a ticket for it. Here are the relevant changes: [fix Data.Map.updateAt Bertram Felgenhauer <int-e@gmx.de>**20070718150340 See http://haskell.org/pipermail/libraries/2007-July/007785.html for a piece of code triggering the bug. updateAt threw away parts of the tree making up the map. ] { hunk ./Data/Map.hs 526 - LT -> updateAt f i l - GT -> updateAt f (i-sizeL-1) r + LT -> balance kx x (updateAt f i l) r + GT -> balance kx x l (updateAt f (i-sizeL-1) r) } Andriy ____________________________________________________________________________________ Park yourself in front of a world of choices in alternative vehicles. Visit the Yahoo! Auto Green Center. http://autos.yahoo.com/green_center/