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diff --git a/src/Erebos/Storage/Merge.hs b/src/Erebos/Storage/Merge.hs
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+++ b/src/Erebos/Storage/Merge.hs
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+module Erebos.Storage.Merge (
+    Mergeable(..),
+    merge, storeMerge,
+
+    Generation,
+    showGeneration,
+    compareGeneration, generationMax,
+    storedGeneration,
+
+    generations,
+    ancestors,
+    precedes,
+    precedesOrEquals,
+    filterAncestors,
+    storedRoots,
+    walkAncestors,
+
+    findProperty,
+    findPropertyFirst,
+) where
+
+import Control.Concurrent.MVar
+
+import Data.ByteString.Char8 qualified as BC
+import Data.HashTable.IO qualified as HT
+import Data.Kind
+import Data.List
+import Data.Maybe
+import Data.Set (Set)
+import Data.Set qualified as S
+
+import System.IO.Unsafe (unsafePerformIO)
+
+import Erebos.Storage
+import Erebos.Storage.Internal
+import Erebos.Util
+
+class Storable (Component a) => Mergeable a where
+    type Component a :: Type
+    mergeSorted :: [Stored (Component a)] -> a
+    toComponents :: a -> [Stored (Component a)]
+
+instance Mergeable [Stored Object] where
+    type Component [Stored Object] = Object
+    mergeSorted = id
+    toComponents = id
+
+merge :: Mergeable a => [Stored (Component a)] -> a
+merge [] = error "merge: empty list"
+merge xs = mergeSorted $ filterAncestors xs
+
+storeMerge :: (Mergeable a, Storable a) => [Stored (Component a)] -> IO (Stored a)
+storeMerge [] = error "merge: empty list"
+storeMerge xs@(Stored ref _ : _) = wrappedStore (refStorage ref) $ mergeSorted $ filterAncestors xs
+
+previous :: Storable a => Stored a -> [Stored a]
+previous (Stored ref _) = case load ref of
+    Rec items | Just (RecRef dref) <- lookup (BC.pack "SDATA") items
+              , Rec ditems <- load dref ->
+                    map wrappedLoad $ catMaybes $ map (\case RecRef r -> Just r; _ -> Nothing) $
+                        map snd $ filter ((`elem` [ BC.pack "SPREV", BC.pack "SBASE" ]) . fst) ditems
+
+              | otherwise ->
+                    map wrappedLoad $ catMaybes $ map (\case RecRef r -> Just r; _ -> Nothing) $
+                        map snd $ filter ((`elem` [ BC.pack "PREV", BC.pack "BASE" ]) . fst) items
+    _ -> []
+
+
+nextGeneration :: [Generation] -> Generation
+nextGeneration = foldl' helper (Generation 0)
+    where helper (Generation c) (Generation n) | c <= n    = Generation (n + 1)
+                                               | otherwise = Generation c
+
+showGeneration :: Generation -> String
+showGeneration (Generation x) = show x
+
+compareGeneration :: Generation -> Generation -> Maybe Ordering
+compareGeneration (Generation x) (Generation y) = Just $ compare x y
+
+generationMax :: Storable a => [Stored a] -> Maybe (Stored a)
+generationMax (x : xs) = Just $ snd $ foldl' helper (storedGeneration x, x) xs
+    where helper (mg, mx) y = let yg = storedGeneration y
+                               in case compareGeneration mg yg of
+                                       Just LT -> (yg, y)
+                                       _       -> (mg, mx)
+generationMax [] = Nothing
+
+storedGeneration :: Storable a => Stored a -> Generation
+storedGeneration x =
+    unsafePerformIO $ withMVar (stRefGeneration $ refStorage $ storedRef x) $ \ht -> do
+        let doLookup y = HT.lookup ht (refDigest $ storedRef y) >>= \case
+                Just gen -> return gen
+                Nothing -> do
+                    gen <- nextGeneration <$> mapM doLookup (previous y)
+                    HT.insert ht (refDigest $ storedRef y) gen
+                    return gen
+        doLookup x
+
+
+generations :: Storable a => [Stored a] -> [Set (Stored a)]
+generations = unfoldr gen . (,S.empty)
+    where gen (hs, cur) = case filter (`S.notMember` cur) $ previous =<< hs of
+              []    -> Nothing
+              added -> let next = foldr S.insert cur added
+                        in Just (next, (added, next))
+
+ancestors :: Storable a => [Stored a] -> Set (Stored a)
+ancestors = last . (S.empty:) . generations
+
+precedes :: Storable a => Stored a -> Stored a -> Bool
+precedes x y = not $ x `elem` filterAncestors [x, y]
+
+precedesOrEquals :: Storable a => Stored a -> Stored a -> Bool
+precedesOrEquals x y = filterAncestors [ x, y ] == [ y ]
+
+filterAncestors :: Storable a => [Stored a] -> [Stored a]
+filterAncestors [x] = [x]
+filterAncestors xs = let xs' = uniq $ sort xs
+                      in helper xs' xs'
+    where helper remains walk = case generationMax walk of
+                                     Just x -> let px = previous x
+                                                   remains' = filter (\r -> all (/=r) px) remains
+                                                in helper remains' $ uniq $ sort (px ++ filter (/=x) walk)
+                                     Nothing -> remains
+
+storedRoots :: Storable a => Stored a -> [Stored a]
+storedRoots x = do
+    let st = refStorage $ storedRef x
+    unsafePerformIO $ withMVar (stRefRoots st) $ \ht -> do
+        let doLookup y = HT.lookup ht (refDigest $ storedRef y) >>= \case
+                Just roots -> return roots
+                Nothing -> do
+                    roots <- case previous y of
+                        [] -> return [refDigest $ storedRef y]
+                        ps -> map (refDigest . storedRef) . filterAncestors . map (wrappedLoad @Object . Ref st) . concat <$> mapM doLookup ps
+                    HT.insert ht (refDigest $ storedRef y) roots
+                    return roots
+        map (wrappedLoad . Ref st) <$> doLookup x
+
+walkAncestors :: (Storable a, Monoid m) => (Stored a -> m) -> [Stored a] -> m
+walkAncestors f = helper . sortBy cmp
+  where
+    helper (x : y : xs) | x == y = helper (x : xs)
+    helper (x : xs) = f x <> helper (mergeBy cmp (sortBy cmp (previous x)) xs)
+    helper [] = mempty
+
+    cmp x y = case compareGeneration (storedGeneration x) (storedGeneration y) of
+                   Just LT -> GT
+                   Just GT -> LT
+                   _ -> compare x y
+
+findProperty :: forall a b. Storable a => (a -> Maybe b) -> [Stored a] -> [b]
+findProperty sel = map (fromJust . sel . fromStored) . filterAncestors . (findPropHeads sel =<<)
+
+findPropertyFirst :: forall a b. Storable a => (a -> Maybe b) -> [Stored a] -> Maybe b
+findPropertyFirst sel = fmap (fromJust . sel . fromStored) . listToMaybe . filterAncestors . (findPropHeads sel =<<)
+
+findPropHeads :: forall a b. Storable a => (a -> Maybe b) -> Stored a -> [Stored a]
+findPropHeads sel sobj | Just _ <- sel $ fromStored sobj = [sobj]
+                       | otherwise = findPropHeads sel =<< previous sobj