diff --git a/TODO.md b/TODO.md
--- a/TODO.md
+++ b/TODO.md
@@ -3,18 +3,13 @@
 
 Here is a list of things TO DO for express:
 
-* release on Hackage -- this should coincide with a new release for both
-  Speculate and Extrapolate.
-
-
-* review `Data.Express` haddock
+* review Haddock of `Data.Express`
 
-* document the `Instances` module
+* document the `Instances` module,
+  including note about linear time on searches
 
 * test the `Instances` module
 
 * sweep occurrences of `TODO:` throughout source files
 
 * Document `test/Test.ListableExpr` module thoroughly;
-
-
diff --git a/express.cabal b/express.cabal
--- a/express.cabal
+++ b/express.cabal
@@ -1,7 +1,7 @@
 -- Cabal file for express
-name:                express
-version:             0.1.0
-synopsis:            Express
+name: express
+version: 0.1.1
+synopsis: Dynamically-typed expressions involving applications and variables.
 description:
   Express is a library for manipulating dynamically typed Haskell expressions.
   It's like @ Data.Dynamic @ but with support for encoding applications and
@@ -12,14 +12,14 @@
   @ Expr @s.  See the README and Haddock documentation for more details.
 
 
-homepage:            https://github.com/rudymatela/express#readme
-license:             BSD3
-license-file:        LICENSE
-author:              Rudy Matela <rudy@matela.com.br>
-maintainer:          Rudy Matela <rudy@matela.com.br>
-category:            Testing
-build-type:          Simple
-cabal-version:       1.18
+homepage: https://github.com/rudymatela/express#readme
+license: BSD3
+license-file: LICENSE
+author:     Rudy Matela <rudy@matela.com.br>
+maintainer: Rudy Matela <rudy@matela.com.br>
+category: Data
+build-type: Simple
+cabal-version: 1.18
 
 extra-doc-files: README.md
                , TODO.md
@@ -57,7 +57,7 @@
 source-repository this
   type:           git
   location:       https://github.com/rudymatela/express
-  tag:            v0.1.0
+  tag:            v0.1.1
 
 library
   exposed-modules:     Data.Express
diff --git a/src/Data/Express/Utils/List.hs b/src/Data/Express/Utils/List.hs
--- a/src/Data/Express/Utils/List.hs
+++ b/src/Data/Express/Utils/List.hs
@@ -9,6 +9,7 @@
 {-# LANGUAGE CPP #-}
 module Data.Express.Utils.List
   ( nubSort
+  , nubSortBy
   , isPermutationOf
   , isSubsetOf
   , isNub
@@ -44,6 +45,15 @@
   nnub [] = []
   nnub [x] = [x]
   nnub (x:xs) = x : nnub (dropWhile (==x) xs)
+
+nubSortBy :: (a -> a -> Ordering) -> [a] -> [a]
+nubSortBy cmp  =  nnub . sortBy cmp
+  where
+  x -==- y  =  x `cmp` y == EQ
+  -- linear nub of adjacent values
+  nnub [] = []
+  nnub [x] = [x]
+  nnub (x:xs) = x : nnub (dropWhile (-==-x) xs)
 
 -- | /O(n log n)/.
 -- Checks that all elements of the first list are elements of the second.
diff --git a/src/Data/Express/Utils/Typeable.hs b/src/Data/Express/Utils/Typeable.hs
--- a/src/Data/Express/Utils/Typeable.hs
+++ b/src/Data/Express/Utils/Typeable.hs
@@ -22,6 +22,8 @@
   , funTyCon
   , compareTy
   , elementTy
+  , typesIn
+  , typesInList
   , (->::)
   , module Data.Typeable
   )
@@ -29,6 +31,7 @@
 
 import Data.Typeable
 import Data.Monoid ((<>))
+import Data.Express.Utils.List
 
 -- Different versions of Typeable/GHC provide different orderings for TypeReps.
 -- The following is a version independent ordering, with the following
@@ -114,6 +117,46 @@
 
 mkCompareTy :: TypeRep -> TypeRep
 mkCompareTy a = a ->:: a ->:: orderingTy
+
+-- | /O(n)/.
+-- Return all sub types of a given type including itself.
+--
+-- > > typesIn $ typeOf (undefined :: Int)
+-- > [Int]
+--
+-- > > typesIn $ typeOf (undefined :: Bool)
+-- > [Bool]
+--
+-- > > typesIn $ typeOf (undefined :: [Int])
+-- > [ Int
+-- > , [Int]
+-- > ]
+--
+-- > > typesIn $ typeOf (undefined :: Int -> Int -> Int)
+-- > [ Int
+-- > , Int -> Int
+-- > , Int -> Int -> Int
+-- > ]
+--
+-- > > typesIn $ typeOf (undefined :: Int -> [Int] -> [Int])
+-- > [ Int
+-- > , [Int]
+-- > , [Int] -> [Int]
+-- > , Int -> [Int] -> [Int]
+-- > ]
+--
+-- > > typesIn $ typeOf (undefined :: Maybe Bool)
+-- > [ Bool
+-- > , Maybe Bool
+-- > ]
+typesIn :: TypeRep -> [TypeRep]
+typesIn t  =  typesInList [t]
+
+typesInList :: [TypeRep] -> [TypeRep]
+typesInList ts  =  nubSortBy compareTy $ tins ts []
+  where
+  tin t  =  (t:) . tins (typeRepArgs t)
+  tins ts  =  foldr (.) id (map tin ts)
 
 -- | An infix alias for 'mkFunTy'.  It is right associative.
 (->::) :: TypeRep -> TypeRep -> TypeRep
diff --git a/test/map.hs b/test/map.hs
--- a/test/map.hs
+++ b/test/map.hs
@@ -90,6 +90,12 @@
   , (xx -+- yy) //- [(yy,yy -+- zz),(xx,xx -+- yy)]
     == (xx -+- yy) -+- (yy -+- zz)
 
+  , ((xx -+- yy) -+- zz) // [(xx -+- yy, zero)] == (zero -+- zz)
+  , (xx -+- (yy -+- zz)) // [(xx -+- yy, zero)] == (xx -+- (yy -+- zz))
+
+  , holds n $ \(SameTypeE e1 e2)   ->          e1 // [(e1,e2)] == e2
+  , holds n $ \(IntE e1) (IntE e2) -> (e1 -+- e1) // [(e1,e2)] == (e2 -+- e2)
+
   , holds n $ \e -> renameVarsBy id e == e
   , holds n $ \c e -> (renameVarsBy tail . renameVarsBy (c:)) e == e
   , renameVarsBy (++ "1") (xx -+- yy) == (var "x1" int -+- var "y1" int)
diff --git a/test/utils.hs b/test/utils.hs
--- a/test/utils.hs
+++ b/test/utils.hs
@@ -24,6 +24,53 @@
   , show (mkCompareTy boolTy) == "Bool -> Bool -> Ordering"
   , show (mkCompareTy intTy)  == "Int -> Int -> Ordering"
 
+  , showTypesInTypeOf (u :: Int)    == ["Int"]
+  , showTypesInTypeOf (u :: Bool)   == ["Bool"]
+  , showTypesInTypeOf (u :: [Int])  == ["Int", "[Int]"]
+  , showTypesInTypeOf (u :: [Bool]) == ["Bool", "[Bool]"]
+  , showTypesInTypeOf (u :: (Int,Int))     == ["Int", "(Int,Int)"]
+  , showTypesInTypeOf (u :: (Bool,Bool))   == ["Bool", "(Bool,Bool)"]
+  , showTypesInTypeOf (u :: (Int,Bool))    == ["Bool", "Int", "(Int,Bool)"]
+  , showTypesInTypeOf (u :: Maybe Integer) == ["Integer", "Maybe Integer"]
+  , showTypesInTypeOf (u :: Int -> Int)    == ["Int", "Int -> Int"]
+  , showTypesInTypeOf (u :: Int -> Bool)   == ["Bool", "Int", "Int -> Bool"]
+
+  , showTypesInTypeOf (u :: Int -> Int -> Int)
+    == [ "Int"
+       , "Int -> Int"
+       , "Int -> Int -> Int"
+       ]
+
+  , showTypesInTypeOf (u :: Either String ())
+    == [ "()"
+       , "Char"
+       , "[Char]"
+       , "Either [Char] ()"
+       ]
+
+  , showTypesInTypeOf (u :: Either String Bool -> Maybe Int -> Int -> Bool)
+    == [ "Bool"
+       , "Char"
+       , "Int"
+       , "Maybe Int"
+       , "[Char]"
+       , "Either [Char] Bool"
+       , "Int -> Bool"
+       , "Maybe Int -> Int -> Bool"
+       , "Either [Char] Bool -> Maybe Int -> Int -> Bool"
+       ]
+
+  , map show (typesInList [typeOf (u :: Int), typeOf (u :: Bool)])
+    == [ "Bool"
+       , "Int"
+       ]
+
+  , map show (typesInList [typeOf (u :: Int), typeOf (u :: Int -> Bool)])
+    == [ "Bool"
+       , "Int"
+       , "Int -> Bool"
+       ]
+
   , primeCycle [] == []
   , ["x", "y", "z", "x'", "y'", "z'", "x''"] `isPrefixOf` primeCycle ["x","y","z"]
   , ["x","x'","x''","x'''","x''''","x'''''"] `isPrefixOf` primeCycle ["x"]
@@ -51,3 +98,9 @@
   , ["thingAndThing", "thingAndThing'", "thingAndThing''", "thingAndThing'''"]
     `isPrefixOf` variableNamesFromTemplate "thingAndThing"
   ]
+
+u :: a
+u  =  undefined
+
+showTypesInTypeOf :: Typeable a => a -> [String]
+showTypesInTypeOf  =  map show . typesIn . typeOf