diff --git a/oi.cabal b/oi.cabal
--- a/oi.cabal
+++ b/oi.cabal
@@ -1,5 +1,5 @@
 Name:			oi
-Version:		0.2.0.1
+Version:		0.2.1.0
 Category:		Data
 Synopsis:		Library for purely functional lazy interactions with the outer world.
 Description:		This package implements a data structure and operations on it for writing interactive program with no imperative flavor of IO monads.
@@ -20,7 +20,7 @@
 Library
   Default-Language:         Haskell2010
   Hs-Source-Dirs:	    src/
-  Build-Depends:	    base >= 4.5 && < 5, parallel, comonad, filepath
+  Build-Depends:	    base >= 4.5 && < 5, parallel, comonad >= 3, filepath
   GHC-Options:		    -Wall -O0
   Exposed-modules:	    Data.OI
                            ,Data.OI.Internal
diff --git a/sample/recdircs.hs b/sample/recdircs.hs
--- a/sample/recdircs.hs
+++ b/sample/recdircs.hs
@@ -14,7 +14,7 @@
 main = runInteraction pmain
 
 pmain :: (([String], [(Bool, IOResult [FilePath])]), ()) :-> ()
-pmain = ((args |> head) |/| getDirCsRec) |> snd |/| putStrOI . unlines
+pmain = (((args >>> head) |/| getDirCsRec) >>> snd) |/| putStrOI . unlines
 
 putStrOI :: String -> () :-> ()
 putStrOI = iooi . putStr
@@ -23,7 +23,7 @@
 isDirectory = iooi . doesDirectoryExist
 
 getDirCs' :: FilePath -> IOResult [FilePath] :-> [FilePath]
-getDirCs' fp = iooi'  (getDirectoryContents fp) |> valid
+getDirCs' fp = iooi'  (getDirectoryContents fp) >>> valid
 
 valid :: IOResult [FilePath] -> [FilePath]
 valid (Success fps) = filter (flip notElem [".",".."]) fps
diff --git a/src/Data/OI/Combinator.hs b/src/Data/OI/Combinator.hs
--- a/src/Data/OI/Combinator.hs
+++ b/src/Data/OI/Combinator.hs
@@ -12,13 +12,14 @@
 module Data.OI.Combinator
   (
    -- * Utility functions
-   (|>)
-  ,choice
+   choice
    -- * Interaction Combinators
   ,(|:|)
   ,(|>|),(|/|)
   ,(|><|)
    -- * Iteration
+  ,sequenceOI
+  ,foldOI
   ,mapOI
   ,zipWithOI
   ,zipWithOI'
@@ -62,11 +63,19 @@
   (a,b) -> (c,d) where (q,c) = f a p; (p,d) = g b q
 
 -- | Iteration
+foldOI :: (a :-> (b -> b)) -> b -> ([a] :-> b)
+foldOI op z xxs = case deList xxs of
+  Just (x,xs) -> x `op` foldOI op z xs
+  _           -> z
 
-mapOI :: (a :-> b) -> ([a] :-> [b])
-mapOI f os = case deList os of 
-  Just (x,xs) -> f x : mapOI f xs
+sequenceOI :: [a :-> b] -> [a] :-> [b]
+sequenceOI (f:fs) oos = case deList oos of
+  Just (o,os) -> f o : sequenceOI fs os
   _           -> []
+sequenceOI _ _ = []
+
+mapOI :: (a :-> b) -> ([a] :-> [b])
+mapOI f = sequenceOI (repeat f)
 
 zipWithOI :: (a -> (b :-> c)) -> ([a] -> ([b] :-> [c]))
 zipWithOI _ [] _ = []
diff --git a/src/Data/OI/Internal.hs b/src/Data/OI/Internal.hs
--- a/src/Data/OI/Internal.hs
+++ b/src/Data/OI/Internal.hs
@@ -49,14 +49,14 @@
 import Prelude hiding ((.),id,catch)
 
 -- | Datatype for intermediating interaction: 
--- @OI@ has two states, non-expressed and exressed. 
+-- @OI@ has two states (programmer cannot distinguish), non-expressed and exressed.
 -- `Non-expressed' indicates that no computation is assigned.
 -- In other words, it's value is never denotated by any expression.
 -- So, if you refer the value then the process will be suspended 
 -- until other process determins the value.
 -- Non-expressed value can be determined to become 'expressed' for a value by a expression at most once.
 -- `Expressed' indicates that some computation is assigned for the value.
--- And expressed values are never changed.
+-- Once expressed, the value never be back to non-expressed nor be changed.
 data OI a = OI (LeftValueOf a) (RightValueOf a)
 
 -- | Interaction (a function from a intermediating type to another type) type
@@ -70,11 +70,9 @@
   return = (##)
   (>>=)  = flip ($) . (??)
 
-instance Extend OI where
-  duplicate = (##)
-
 instance Comonad OI where
   extract = (??)
+  duplicate = (##)
 
 -- | Dereference operator
 (??) :: OI a -> a