diff --git a/README.markdown b/README.markdown
index 2a547d2..0af8863 100644
--- a/README.markdown
+++ b/README.markdown
@@ -16,7 +16,7 @@ The exercises take into account various possible goals. For example, if you wish
 to study the history of lenses, then build up to the most recent theories, it is
 best to start at the `Lets.GetSetLens` module. If you wish to derive the
 structure of lenses from first principles, then derive the more modern theories,
-start at the `Lets.Lens.Lens` module.
+start at the `Lets.Lens` module.
 
 Exercises can be recognised by filling in a function body that has a placeholder
 of `error "todo: <function-name>"`.
@@ -49,7 +49,7 @@ This series of exercises introduces a new representation of lenses, first
 described by Twan van Laarhoven. This representation also introduces a
 generalisation of lenses to permit *polymorphic update* of structures.
 
-##### `Lets.Lens.Lens`
+##### `Lets.Lens`
 
 This series of exercises starts at first principles to derive the concept of a
 lens, as it was first described by Twan van Laarhoven. The derivation then goes
diff --git a/lets-lens.cabal b/lets-lens.cabal
index aa12f69..a1d755e 100644
--- a/lets-lens.cabal
+++ b/lets-lens.cabal
@@ -39,13 +39,12 @@ library
   hs-source-dirs:     src
 
   exposed-modules:    Lets
+                      Lets.Choice
                       Lets.Data
                       Lets.GetSetLens
                       Lets.Lens
-                      Lets.Lens.Choice
-                      Lets.Lens.Lens
-                      Lets.Lens.Profunctor
                       Lets.OpticPolyLens
+                      Lets.Profunctor
                       Lets.StoreLens
                       
 test-suite            doctests
diff --git a/src/Lets/Lens/Choice.hs b/src/Lets/Choice.hs
similarity index 92%
rename from src/Lets/Lens/Choice.hs
rename to src/Lets/Choice.hs
index a277a75..a71b486 100644
--- a/src/Lets/Lens/Choice.hs
+++ b/src/Lets/Choice.hs
@@ -1,9 +1,9 @@
-module Lets.Lens.Choice (
+module Lets.Choice (
   Choice(..)
 ) where
 
 import Lets.Data
-import Lets.Lens.Profunctor
+import Lets.Profunctor
 
 diswap ::
   Profunctor p =>
diff --git a/src/Lets/Lens.hs b/src/Lets/Lens.hs
index daa878c..bf5c8d5 100644
--- a/src/Lets/Lens.hs
+++ b/src/Lets/Lens.hs
@@ -1,7 +1,788 @@
+{-# LANGUAGE RankNTypes #-}
+
 module Lets.Lens (
-  module L
+  fmapT
+, over
+, fmapTAgain
+, Set
+, sets
+, mapped
+, set
+, foldMapT
+, foldMapOf
+, foldMapTAgain
+, Fold
+, folds
+, folded
+, Get
+, get
+, Traversal
+, both
+, traverseLeft
+, traverseRight
+, Traversal'
+, Lens
+, Prism
+, _Left
+, _Right
+, prism
+, _Just
+, _Nothing
+, setP
+, getP
+, Prism'
+, modify
+, (%~)
+, (.~)
+, fmodify
+, (|=)
+, fstL
+, sndL
+, mapL
+, setL
+, compose
+, (|.)
+, identity
+, product
+, (***)
+, choice
+, (|||)
+, Lens'
+, cityL
+, stateL
+, countryL
+, streetL
+, suburbL
+, localityL
+, ageL
+, nameL
+, addressL
+, intAndIntL
+, intAndL
+, getSuburb
+, setStreet
+, getAgeAndCountry
+, setCityAndLocality
+, getSuburbOrCity
+, setStreetOrState
+, modifyCityUppercase
+, modifyIntAndLengthEven
+, traverseLocality
+, intOrIntP
+, intOrP
+, intOrLengthEven
 ) where
 
-import Lets.Lens.Choice as L
-import Lets.Lens.Lens as L
-import Lets.Lens.Profunctor as L
+import Control.Applicative(Applicative((<*>), pure))
+import Data.Bool(bool)
+import Data.Char(toUpper)
+import Data.Foldable(Foldable(foldMap))
+import Data.Functor((<$>))
+import Data.Map(Map)
+import qualified Data.Map as Map(insert, delete, lookup)
+import Data.Monoid(Monoid)
+import qualified Data.Set as Set(Set, insert, delete, member)
+import Data.Traversable(Traversable(traverse))
+import Lets.Data(AlongsideLeft(AlongsideLeft, getAlongsideLeft), AlongsideRight(AlongsideRight, getAlongsideRight), Identity(Identity, getIdentity), Const(Const, getConst), Tagged(Tagged, getTagged), IntOr(IntOrIs, IntOrIsNot), IntAnd(IntAnd), Person(Person), Locality(Locality), Address(Address))
+import Lets.Choice(Choice(left, right))
+import Lets.Profunctor(Profunctor(dimap))
+import Prelude hiding (product)
+
+-- $setup
+-- >>> import qualified Data.Map as Map(fromList)
+-- >>> import qualified Data.Set as Set(fromList)
+-- >>> import Data.Char(ord)
+
+-- Let's remind ourselves of Traversable, noting Foldable and Functor.
+--
+-- class (Foldable t, Functor t) => Traversable t where
+--   traverse ::
+--     Applicative f => 
+--     (a -> f b)
+--     -> t a
+--     -> f (t b)
+
+-- | Observe that @fmap@ can be recovered from @traverse@ using @Identity@.
+--
+-- /Reminder:/ fmap :: Functor t => (a -> b) -> t a -> t b
+fmapT ::
+  Traversable t =>
+  (a -> b)
+  -> t a
+  -> t b
+fmapT =
+  error "todo: fmapT"
+
+-- | Let's refactor out the call to @traverse@ as an argument to @fmapT@.
+over :: 
+  ((a -> Identity b) -> s -> Identity t)
+  -> (a -> b)
+  -> s
+  -> t
+over =
+  error "todo: over"
+
+-- | Here is @fmapT@ again, passing @traverse@ to @over@.
+fmapTAgain ::
+  Traversable t =>
+  (a -> b)
+  -> t a
+  -> t b
+fmapTAgain =
+  error "todo: fmapTAgain"
+
+-- | Let's create a type-alias for this type of function.
+type Set s t a b =
+  (a -> Identity b)
+  -> s
+  -> Identity t
+
+-- | Let's write an inverse to @over@ that does the @Identity@ wrapping &
+-- unwrapping.
+sets ::
+  ((a -> b) -> s -> t)
+  -> Set s t a b  
+sets =
+  error "todo: sets"
+
+mapped ::
+  Functor f =>
+  Set (f a) (f b) a b
+mapped =
+  error "todo: mapped"
+
+set ::
+  Set s t a b
+  -> s
+  -> b
+  -> t
+set =
+  error "todo: set"
+
+----
+
+-- | Observe that @fmap@ can be recovered from @traverse@ using @Identity@.
+--
+-- /Reminder:/ foldMap :: (Foldable t, Monoid b) => (a -> b) -> t a -> b
+foldMapT ::
+  (Traversable t, Monoid b) =>
+  (a -> b)
+  -> t a
+  -> b
+foldMapT =
+  error "todo: foldMapT"
+
+-- | Let's refactor out the call to @traverse@ as an argument to @foldMapT@.
+foldMapOf ::
+  ((a -> Const r b) -> s -> Const r t)
+  -> (a -> r)
+  -> s
+  -> r
+foldMapOf =
+  error "todo: foldMapOf"
+
+-- | Here is @foldMapT@ again, passing @traverse@ to @foldMapOf@.
+foldMapTAgain ::
+  (Traversable t, Monoid b) =>
+  (a -> b)
+  -> t a
+  -> b
+foldMapTAgain =
+  error "todo: foldMapTAgain"
+
+-- | Let's create a type-alias for this type of function.
+type Fold s t a b =
+  forall r.
+  Monoid r =>
+  (a -> Const r b)
+  -> s
+  -> Const r t
+
+-- | Let's write an inverse to @foldMapOf@ that does the @Const@ wrapping &
+-- unwrapping.
+folds ::
+  ((a -> b) -> s -> t)
+  -> (a -> Const b a)
+  -> s
+  -> Const t s
+folds =
+  error "todo: folds"
+
+folded ::
+  Foldable f =>
+  Fold (f a) (f a) a a
+folded =
+  error "todo: folded"
+
+----
+
+-- | @Get@ is like @Fold@, but without the @Monoid@ constraint.
+type Get r s a =
+  (a -> Const r a)
+  -> s
+  -> Const r s
+
+get ::
+  Get a s a
+  -> s
+  -> a
+get =
+  error "todo: get"
+
+----
+
+-- | Let's generalise @Identity@ and @Const r@ to any @Applicative@ instance.
+type Traversal s t a b =
+  forall f.
+  Applicative f =>
+  (a -> f b)
+  -> s
+  -> f t
+
+-- | Traverse both sides of a pair.
+both ::
+  Traversal (a, a) (b, b) a b
+both =
+  error "todo: both"
+
+-- | Traverse the left side of @Either@.
+traverseLeft ::
+  Traversal (Either a x) (Either b x) a b
+traverseLeft =
+  error "todo: traverseLeft"
+
+-- | Traverse the right side of @Either@.
+traverseRight ::
+  Traversal (Either x a) (Either x b) a b
+traverseRight =
+  error "todo: traverseRight"
+
+type Traversal' a b =
+  Traversal a a b b
+
+----
+
+-- | @Const r@ is @Applicative@, if @Monoid r@, however, without the @Monoid@
+-- constraint (as in @Get@), the only shared abstraction between @Identity@ and
+-- @Const r@ is @Functor@.
+--
+-- Consequently, we arrive at our lens derivation:
+type Lens s t a b =
+  forall f.
+  Functor f =>
+  (a -> f b)
+  -> s
+  -> f t
+
+----
+
+-- | A prism is a less specific type of traversal.
+type Prism s t a b =
+  forall p f.
+  (Choice p, Applicative f) =>
+  p a (f b)
+  -> p s (f t)
+
+_Left ::
+  Prism (Either a x) (Either b x) a b
+_Left =
+  error "todo: _Left"
+
+_Right ::
+  Prism (Either x a) (Either x b) a b 
+_Right =
+  error "todo: _Right"
+
+prism ::
+  (b -> t)
+  -> (s -> Either t a)
+  -> Prism s t a b
+prism =
+  error "todo: prism"
+
+_Just ::
+  Prism (Maybe a) (Maybe b) a b
+_Just =
+  error "todo: _Just"
+
+_Nothing ::
+  Prism (Maybe a) (Maybe a) () ()
+_Nothing =
+  error "todo: _Nothing"
+
+setP ::
+  Prism s t a b
+  -> s
+  -> Either t a
+setP =
+  error "todo: setP"
+
+getP ::
+  Prism s t a b
+  -> b
+  -> t
+getP =
+  error "todo: getP"
+
+type Prism' a b =
+  Prism a a b b
+
+----
+
+-- |
+--
+-- >>> modify fstL (+1) (0 :: Int, "abc")
+-- (1,"abc")
+--
+-- >>> modify sndL (+1) ("abc", 0 :: Int)
+-- ("abc",1)
+--
+-- prop> let types = (x :: Int, y :: String) in modify fstL id (x, y) == (x, y)
+--
+-- prop> let types = (x :: Int, y :: String) in modify sndL id (x, y) == (x, y)
+modify ::
+  Lens s t a b
+  -> (a -> b)
+  -> s
+  -> t
+modify =
+  error "todo: modify"
+
+-- | An alias for @modify@.
+(%~) ::
+  Lens s t a b
+  -> (a -> b)
+  -> s
+  -> t
+(%~) =
+  modify
+
+infixr 4 %~
+
+-- |
+--
+-- >>> fstL .~ 1 $ (0 :: Int, "abc")
+-- (1,"abc")
+--
+-- >>> sndL .~ 1 $ ("abc", 0 :: Int)
+-- ("abc",1)
+--
+-- prop> let types = (x :: Int, y :: String) in set fstL (x, y) z == (fstL .~ z $ (x, y))
+--
+-- prop> let types = (x :: Int, y :: String) in set sndL (x, y) z == (sndL .~ z $ (x, y))
+(.~) ::
+  Lens s t a b
+  -> b
+  -> s
+  -> t
+(.~) =
+  error "todo: (.~)"
+
+infixl 5 .~
+
+-- |
+--
+-- >>> fmodify fstL (+) (5 :: Int, "abc") 8
+-- (13,"abc")
+--
+-- >>> fmodify fstL (\n -> bool Nothing (Just (n * 2)) (even n)) (10, "abc")
+-- Just (20,"abc")
+--
+-- >>> fmodify fstL (\n -> bool Nothing (Just (n * 2)) (even n)) (11, "abc")
+-- Nothing
+fmodify ::
+  Functor f =>
+  Lens s t a b
+  -> (a -> f b)
+  -> s
+  -> f t 
+fmodify =
+  error "todo: fmodify"
+
+-- |
+--
+-- >>> fstL |= Just 3 $ (7, "abc")
+-- Just (3,"abc")
+--
+-- >>> (fstL |= (+1) $ (3, "abc")) 17
+-- (18,"abc")
+(|=) ::
+  Functor f =>
+  Lens s t a b
+  -> f b
+  -> s
+  -> f t
+(|=) =
+  error "todo: (|=)"
+
+infixl 5 |=
+
+-- |
+--
+-- >>> modify fstL (*10) (3, "abc")
+-- (30,"abc")
+fstL ::
+  Lens (a, x) (b, x) a b
+fstL =
+  error "todo: fstL"
+
+-- |
+--
+-- >>> modify sndL (++ "def") (13, "abc")
+-- (13,"abcdef")
+sndL ::
+  Lens (x, a) (x, b) a b
+sndL =
+  error "todo: sndL"
+
+-- |
+--
+-- >>> get (mapL 3) (Map.fromList (map (\c -> (ord c - 96, c)) ['a'..'d']))
+-- Just 'c'
+--
+-- >>> get (mapL 33) (Map.fromList (map (\c -> (ord c - 96, c)) ['a'..'d']))
+-- Nothing
+--
+-- >>> set (mapL 3) (Map.fromList (map (\c -> (ord c - 96, c)) ['a'..'d'])) (Just 'X')
+-- fromList [(1,'a'),(2,'b'),(3,'X'),(4,'d')]
+--
+-- >>> set (mapL 33) (Map.fromList (map (\c -> (ord c - 96, c)) ['a'..'d'])) (Just 'X')
+-- fromList [(1,'a'),(2,'b'),(3,'c'),(4,'d'),(33,'X')]
+--
+-- >>> set (mapL 3) (Map.fromList (map (\c -> (ord c - 96, c)) ['a'..'d'])) Nothing
+-- fromList [(1,'a'),(2,'b'),(4,'d')]
+--
+-- >>> set (mapL 33) (Map.fromList (map (\c -> (ord c - 96, c)) ['a'..'d'])) Nothing
+-- fromList [(1,'a'),(2,'b'),(3,'c'),(4,'d')]
+mapL ::
+  Ord k =>
+  k
+  -> Lens (Map k v) (Map k v) (Maybe v) (Maybe v)
+mapL =
+  error "todo: mapL"
+
+-- |
+--
+-- >>> get (setL 3) (Set.fromList [1..5])
+-- True
+--
+-- >>> get (setL 33) (Set.fromList [1..5])
+-- False
+--
+-- >>> set (setL 3) (Set.fromList [1..5]) True
+-- fromList [1,2,3,4,5]
+--
+-- >>> set (setL 3) (Set.fromList [1..5]) False
+-- fromList [1,2,4,5]
+--
+-- >>> set (setL 33) (Set.fromList [1..5]) True
+-- fromList [1,2,3,4,5,33]
+--
+-- >>> set (setL 33) (Set.fromList [1..5]) False
+-- fromList [1,2,3,4,5]
+setL ::
+  Ord k =>
+  k
+  -> Lens (Set.Set k) (Set.Set k) Bool Bool
+setL =
+  error "todo: setL"
+
+-- |
+--
+-- >>> get (compose fstL sndL) ("abc", (7, "def"))
+-- 7
+--
+-- >>> set (compose fstL sndL) ("abc", (7, "def")) 8
+-- ("abc",(8,"def"))
+compose ::
+  Lens s t a b
+  -> Lens q r s t
+  -> Lens q r a b
+compose =
+  error "todo: compose"
+
+-- | An alias for @compose@.
+(|.) ::
+  Lens s t a b
+  -> Lens q r s t
+  -> Lens q r a b
+(|.) =
+  compose
+
+infixr 9 |.
+
+-- |
+--
+-- >>> get identity 3
+-- 3
+--
+-- >>> set identity 3 4
+-- 4
+identity ::
+  Lens a b a b
+identity =
+  error "todo: identity"
+
+-- |
+--
+-- >>> get (product fstL sndL) (("abc", 3), (4, "def"))
+-- ("abc","def")
+--
+-- >>> set (product fstL sndL) (("abc", 3), (4, "def")) ("ghi", "jkl")
+-- (("ghi",3),(4,"jkl"))
+product ::
+  Lens s t a b
+  -> Lens q r c d
+  -> Lens (s, q) (t, r) (a, c) (b, d)
+product =
+  error "todo: product"
+
+-- | An alias for @product@.
+(***) ::
+  Lens s t a b
+  -> Lens q r c d
+  -> Lens (s, q) (t, r) (a, c) (b, d)
+(***) =
+  product
+
+infixr 3 ***
+
+-- |
+--
+-- >>> get (choice fstL sndL) (Left ("abc", 7))
+-- "abc"
+--
+-- >>> get (choice fstL sndL) (Right ("abc", 7))
+-- 7
+--
+-- >>> set (choice fstL sndL) (Left ("abc", 7)) "def"
+-- Left ("def",7)
+--
+-- >>> set (choice fstL sndL) (Right ("abc", 7)) 8
+-- Right ("abc",8)
+choice ::
+  Lens s t a b
+  -> Lens q r a b
+  -> Lens (Either s q) (Either t r) a b
+choice =
+  error "todo: choice"
+
+-- | An alias for @choice@.
+(|||) ::
+  Lens s t a b
+  -> Lens q r a b
+  -> Lens (Either s q) (Either t r) a b
+(|||) =
+  choice
+
+infixr 2 |||
+
+----
+
+type Lens' a b =
+  Lens a a b b
+
+cityL ::
+  Lens' Locality String
+cityL p (Locality c t y) =
+  fmap (\c' -> Locality c' t y) (p c)
+
+stateL ::
+  Lens' Locality String
+stateL p (Locality c t y) =
+  fmap (\t' -> Locality c t' y) (p t)
+
+countryL ::
+  Lens' Locality String
+countryL p (Locality c t y) =
+  fmap (\y' -> Locality c t y') (p y)
+
+streetL ::
+  Lens' Address String
+streetL p (Address t s l) =
+  fmap (\t' -> Address t' s l) (p t)
+
+suburbL ::
+  Lens' Address String
+suburbL p (Address t s l) =
+  fmap (\s' -> Address t s' l) (p s)
+
+localityL ::
+  Lens' Address Locality
+localityL p (Address t s l) =
+  fmap (\l' -> Address t s l') (p l)
+
+ageL ::
+  Lens' Person Int
+ageL p (Person a n d) =
+  fmap (\a' -> Person a' n d) (p a)
+
+nameL ::
+  Lens' Person String
+nameL p (Person a n d) =
+  fmap (\n' -> Person a n' d) (p n)
+
+addressL ::
+  Lens' Person Address
+addressL p (Person a n d) =
+  fmap (\d' -> Person a n d') (p d)
+
+intAndIntL ::
+  Lens' (IntAnd a) Int
+intAndIntL p (IntAnd n a) =
+  fmap (\n' -> IntAnd n' a) (p n)
+
+-- lens for polymorphic update
+intAndL ::
+  Lens (IntAnd a) (IntAnd b) a b
+intAndL p (IntAnd n a) =
+  fmap (\a' -> IntAnd n a') (p a)
+
+-- |
+--
+-- >>> get (suburbL |. addressL) fred
+-- "Fredville"
+--
+-- >>> get (suburbL |. addressL) mary
+-- "Maryland"
+getSuburb ::
+  Person
+  -> String
+getSuburb =
+  error "todo: getSuburb"
+
+-- |
+--
+-- >>> setStreet fred "Some Other St"
+-- Person 24 "Fred" (Address "Some Other St" "Fredville" (Locality "Fredmania" "New South Fred" "Fredalia"))
+--
+-- >>> setStreet mary "Some Other St"
+-- Person 28 "Mary" (Address "Some Other St" "Maryland" (Locality "Mary Mary" "Western Mary" "Maristan"))
+setStreet ::
+  Person
+  -> String
+  -> Person
+setStreet =
+  error "todo: setStreet"
+
+-- |
+--
+-- >>> getAgeAndCountry (fred, maryLocality)
+-- (24,"Maristan")
+--
+-- >>> getAgeAndCountry (mary, fredLocality)
+-- (28,"Fredalia")
+getAgeAndCountry ::
+  (Person, Locality)
+  -> (Int, String)
+getAgeAndCountry =
+  error "todo: getAgeAndCountry"
+
+-- |
+--
+-- >>> setCityAndLocality (fred, maryAddress) ("Some Other City", fredLocality)
+-- (Person 24 "Fred" (Address "15 Fred St" "Fredville" (Locality "Some Other City" "New South Fred" "Fredalia")),Address "83 Mary Ln" "Maryland" (Locality "Fredmania" "New South Fred" "Fredalia"))
+--
+-- >>> setCityAndLocality (mary, fredAddress) ("Some Other City", maryLocality)
+-- (Person 28 "Mary" (Address "83 Mary Ln" "Maryland" (Locality "Some Other City" "Western Mary" "Maristan")),Address "15 Fred St" "Fredville" (Locality "Mary Mary" "Western Mary" "Maristan"))
+setCityAndLocality ::
+  (Person, Address) -> (String, Locality) -> (Person, Address)
+setCityAndLocality =
+  error "todo: setCityAndLocality"
+  
+-- |
+--
+-- >>> getSuburbOrCity (Left maryAddress)
+-- "Maryland"
+--
+-- >>> getSuburbOrCity (Right fredLocality)
+-- "Fredmania"
+getSuburbOrCity ::
+  Either Address Locality
+  -> String
+getSuburbOrCity =
+  error "todo: getSuburbOrCity"
+
+-- |
+--
+-- >>> setStreetOrState (Right maryLocality) "Some Other State"
+-- Right (Locality "Mary Mary" "Some Other State" "Maristan")
+--
+-- >>> setStreetOrState (Left fred) "Some Other St"
+-- Left (Person 24 "Fred" (Address "Some Other St" "Fredville" (Locality "Fredmania" "New South Fred" "Fredalia")))
+setStreetOrState ::
+  Either Person Locality
+  -> String
+  -> Either Person Locality
+setStreetOrState =
+  error "todo: setStreetOrState"
+
+-- |
+--
+-- >>> modifyCityUppercase fred
+-- Person 24 "Fred" (Address "15 Fred St" "Fredville" (Locality "FREDMANIA" "New South Fred" "Fredalia"))
+--
+-- >>> modifyCityUppercase mary
+-- Person 28 "Mary" (Address "83 Mary Ln" "Maryland" (Locality "MARY MARY" "Western Mary" "Maristan"))
+modifyCityUppercase ::
+  Person
+  -> Person
+modifyCityUppercase =
+  error "todo: modifyCityUppercase"
+
+-- |
+--
+-- >>> modifyIntAndLengthEven (IntAnd 10 "abc")
+-- IntAnd 10 False
+--
+-- >>> modifyIntAndLengthEven (IntAnd 10 "abcd")
+-- IntAnd 10 True
+modifyIntAndLengthEven ::
+  IntAnd [a]
+  -> IntAnd Bool
+modifyIntAndLengthEven =
+  error "todo: modifyIntAndLengthEven"
+
+----
+
+-- |
+--
+-- >>> over traverseLocality (map toUpper) (Locality "abc" "def" "ghi")
+-- Locality "ABC" "DEF" "GHI"
+traverseLocality ::
+  Traversal' Locality String
+traverseLocality =
+  error "todo: traverseLocality"
+
+-- |
+--
+-- >>> over intOrIntP (*10) (IntOrIs 3)
+-- IntOrIs 30
+--
+-- >>> over intOrIntP (*10) (IntOrIsNot "abc")
+-- IntOrIsNot "abc"
+intOrIntP ::
+  Prism' (IntOr a) Int
+intOrIntP =
+  error "todo: intOrIntP"
+
+intOrP ::
+  Prism (IntOr a) (IntOr b) a b
+intOrP =
+  error "todo: intOrP"
+
+-- |
+--
+-- >> over intOrP (even . length) (IntOrIsNot "abc")
+-- IntOrIsNot False
+--
+-- >>> over intOrP (even . length) (IntOrIsNot "abcd")
+-- IntOrIsNot True
+--
+-- >>> over intOrP (even . length) (IntOrIs 10)
+-- IntOrIs 10
+intOrLengthEven ::
+  IntOr [a]
+  -> IntOr Bool
+intOrLengthEven =
+  error "todo: intOrLengthEven"
diff --git a/src/Lets/Lens/Lens.hs b/src/Lets/Lens/Lens.hs
deleted file mode 100644
index e2cc676..0000000
--- a/src/Lets/Lens/Lens.hs
+++ /dev/null
@@ -1,788 +0,0 @@
-{-# LANGUAGE RankNTypes #-}
-
-module Lets.Lens.Lens (
-  fmapT
-, over
-, fmapTAgain
-, Set
-, sets
-, mapped
-, set
-, foldMapT
-, foldMapOf
-, foldMapTAgain
-, Fold
-, folds
-, folded
-, Get
-, get
-, Traversal
-, both
-, traverseLeft
-, traverseRight
-, Traversal'
-, Lens
-, Prism
-, _Left
-, _Right
-, prism
-, _Just
-, _Nothing
-, setP
-, getP
-, Prism'
-, modify
-, (%~)
-, (.~)
-, fmodify
-, (|=)
-, fstL
-, sndL
-, mapL
-, setL
-, compose
-, (|.)
-, identity
-, product
-, (***)
-, choice
-, (|||)
-, Lens'
-, cityL
-, stateL
-, countryL
-, streetL
-, suburbL
-, localityL
-, ageL
-, nameL
-, addressL
-, intAndIntL
-, intAndL
-, getSuburb
-, setStreet
-, getAgeAndCountry
-, setCityAndLocality
-, getSuburbOrCity
-, setStreetOrState
-, modifyCityUppercase
-, modifyIntAndLengthEven
-, traverseLocality
-, intOrIntP
-, intOrP
-, intOrLengthEven
-) where
-
-import Control.Applicative(Applicative((<*>), pure))
-import Data.Bool(bool)
-import Data.Char(toUpper)
-import Data.Foldable(Foldable(foldMap))
-import Data.Functor((<$>))
-import Data.Map(Map)
-import qualified Data.Map as Map(insert, delete, lookup)
-import Data.Monoid(Monoid)
-import qualified Data.Set as Set(Set, insert, delete, member)
-import Data.Traversable(Traversable(traverse))
-import Lets.Data(AlongsideLeft(AlongsideLeft, getAlongsideLeft), AlongsideRight(AlongsideRight, getAlongsideRight), Identity(Identity, getIdentity), Const(Const, getConst), Tagged(Tagged, getTagged), IntOr(IntOrIs, IntOrIsNot), IntAnd(IntAnd), Person(Person), Locality(Locality), Address(Address))
-import Lets.Lens.Choice(Choice(left, right))
-import Lets.Lens.Profunctor(Profunctor(dimap))
-import Prelude hiding (product)
-
--- $setup
--- >>> import qualified Data.Map as Map(fromList)
--- >>> import qualified Data.Set as Set(fromList)
--- >>> import Data.Char(ord)
-
--- Let's remind ourselves of Traversable, noting Foldable and Functor.
---
--- class (Foldable t, Functor t) => Traversable t where
---   traverse ::
---     Applicative f => 
---     (a -> f b)
---     -> t a
---     -> f (t b)
-
--- | Observe that @fmap@ can be recovered from @traverse@ using @Identity@.
---
--- /Reminder:/ fmap :: Functor t => (a -> b) -> t a -> t b
-fmapT ::
-  Traversable t =>
-  (a -> b)
-  -> t a
-  -> t b
-fmapT =
-  error "todo: fmapT"
-
--- | Let's refactor out the call to @traverse@ as an argument to @fmapT@.
-over :: 
-  ((a -> Identity b) -> s -> Identity t)
-  -> (a -> b)
-  -> s
-  -> t
-over =
-  error "todo: over"
-
--- | Here is @fmapT@ again, passing @traverse@ to @over@.
-fmapTAgain ::
-  Traversable t =>
-  (a -> b)
-  -> t a
-  -> t b
-fmapTAgain =
-  error "todo: fmapTAgain"
-
--- | Let's create a type-alias for this type of function.
-type Set s t a b =
-  (a -> Identity b)
-  -> s
-  -> Identity t
-
--- | Let's write an inverse to @over@ that does the @Identity@ wrapping &
--- unwrapping.
-sets ::
-  ((a -> b) -> s -> t)
-  -> Set s t a b  
-sets =
-  error "todo: sets"
-
-mapped ::
-  Functor f =>
-  Set (f a) (f b) a b
-mapped =
-  error "todo: mapped"
-
-set ::
-  Set s t a b
-  -> s
-  -> b
-  -> t
-set =
-  error "todo: set"
-
-----
-
--- | Observe that @fmap@ can be recovered from @traverse@ using @Identity@.
---
--- /Reminder:/ foldMap :: (Foldable t, Monoid b) => (a -> b) -> t a -> b
-foldMapT ::
-  (Traversable t, Monoid b) =>
-  (a -> b)
-  -> t a
-  -> b
-foldMapT =
-  error "todo: foldMapT"
-
--- | Let's refactor out the call to @traverse@ as an argument to @foldMapT@.
-foldMapOf ::
-  ((a -> Const r b) -> s -> Const r t)
-  -> (a -> r)
-  -> s
-  -> r
-foldMapOf =
-  error "todo: foldMapOf"
-
--- | Here is @foldMapT@ again, passing @traverse@ to @foldMapOf@.
-foldMapTAgain ::
-  (Traversable t, Monoid b) =>
-  (a -> b)
-  -> t a
-  -> b
-foldMapTAgain =
-  error "todo: foldMapTAgain"
-
--- | Let's create a type-alias for this type of function.
-type Fold s t a b =
-  forall r.
-  Monoid r =>
-  (a -> Const r b)
-  -> s
-  -> Const r t
-
--- | Let's write an inverse to @foldMapOf@ that does the @Const@ wrapping &
--- unwrapping.
-folds ::
-  ((a -> b) -> s -> t)
-  -> (a -> Const b a)
-  -> s
-  -> Const t s
-folds =
-  error "todo: folds"
-
-folded ::
-  Foldable f =>
-  Fold (f a) (f a) a a
-folded =
-  error "todo: folded"
-
-----
-
--- | @Get@ is like @Fold@, but without the @Monoid@ constraint.
-type Get r s a =
-  (a -> Const r a)
-  -> s
-  -> Const r s
-
-get ::
-  Get a s a
-  -> s
-  -> a
-get =
-  error "todo: get"
-
-----
-
--- | Let's generalise @Identity@ and @Const r@ to any @Applicative@ instance.
-type Traversal s t a b =
-  forall f.
-  Applicative f =>
-  (a -> f b)
-  -> s
-  -> f t
-
--- | Traverse both sides of a pair.
-both ::
-  Traversal (a, a) (b, b) a b
-both =
-  error "todo: both"
-
--- | Traverse the left side of @Either@.
-traverseLeft ::
-  Traversal (Either a x) (Either b x) a b
-traverseLeft =
-  error "todo: traverseLeft"
-
--- | Traverse the right side of @Either@.
-traverseRight ::
-  Traversal (Either x a) (Either x b) a b
-traverseRight =
-  error "todo: traverseRight"
-
-type Traversal' a b =
-  Traversal a a b b
-
-----
-
--- | @Const r@ is @Applicative@, if @Monoid r@, however, without the @Monoid@
--- constraint (as in @Get@), the only shared abstraction between @Identity@ and
--- @Const r@ is @Functor@.
---
--- Consequently, we arrive at our lens derivation:
-type Lens s t a b =
-  forall f.
-  Functor f =>
-  (a -> f b)
-  -> s
-  -> f t
-
-----
-
--- | A prism is a less specific type of traversal.
-type Prism s t a b =
-  forall p f.
-  (Choice p, Applicative f) =>
-  p a (f b)
-  -> p s (f t)
-
-_Left ::
-  Prism (Either a x) (Either b x) a b
-_Left =
-  error "todo: _Left"
-
-_Right ::
-  Prism (Either x a) (Either x b) a b 
-_Right =
-  error "todo: _Right"
-
-prism ::
-  (b -> t)
-  -> (s -> Either t a)
-  -> Prism s t a b
-prism =
-  error "todo: prism"
-
-_Just ::
-  Prism (Maybe a) (Maybe b) a b
-_Just =
-  error "todo: _Just"
-
-_Nothing ::
-  Prism (Maybe a) (Maybe a) () ()
-_Nothing =
-  error "todo: _Nothing"
-
-setP ::
-  Prism s t a b
-  -> s
-  -> Either t a
-setP =
-  error "todo: setP"
-
-getP ::
-  Prism s t a b
-  -> b
-  -> t
-getP =
-  error "todo: getP"
-
-type Prism' a b =
-  Prism a a b b
-
-----
-
--- |
---
--- >>> modify fstL (+1) (0 :: Int, "abc")
--- (1,"abc")
---
--- >>> modify sndL (+1) ("abc", 0 :: Int)
--- ("abc",1)
---
--- prop> let types = (x :: Int, y :: String) in modify fstL id (x, y) == (x, y)
---
--- prop> let types = (x :: Int, y :: String) in modify sndL id (x, y) == (x, y)
-modify ::
-  Lens s t a b
-  -> (a -> b)
-  -> s
-  -> t
-modify =
-  error "todo: modify"
-
--- | An alias for @modify@.
-(%~) ::
-  Lens s t a b
-  -> (a -> b)
-  -> s
-  -> t
-(%~) =
-  modify
-
-infixr 4 %~
-
--- |
---
--- >>> fstL .~ 1 $ (0 :: Int, "abc")
--- (1,"abc")
---
--- >>> sndL .~ 1 $ ("abc", 0 :: Int)
--- ("abc",1)
---
--- prop> let types = (x :: Int, y :: String) in set fstL (x, y) z == (fstL .~ z $ (x, y))
---
--- prop> let types = (x :: Int, y :: String) in set sndL (x, y) z == (sndL .~ z $ (x, y))
-(.~) ::
-  Lens s t a b
-  -> b
-  -> s
-  -> t
-(.~) =
-  error "todo: (.~)"
-
-infixl 5 .~
-
--- |
---
--- >>> fmodify fstL (+) (5 :: Int, "abc") 8
--- (13,"abc")
---
--- >>> fmodify fstL (\n -> bool Nothing (Just (n * 2)) (even n)) (10, "abc")
--- Just (20,"abc")
---
--- >>> fmodify fstL (\n -> bool Nothing (Just (n * 2)) (even n)) (11, "abc")
--- Nothing
-fmodify ::
-  Functor f =>
-  Lens s t a b
-  -> (a -> f b)
-  -> s
-  -> f t 
-fmodify =
-  error "todo: fmodify"
-
--- |
---
--- >>> fstL |= Just 3 $ (7, "abc")
--- Just (3,"abc")
---
--- >>> (fstL |= (+1) $ (3, "abc")) 17
--- (18,"abc")
-(|=) ::
-  Functor f =>
-  Lens s t a b
-  -> f b
-  -> s
-  -> f t
-(|=) =
-  error "todo: (|=)"
-
-infixl 5 |=
-
--- |
---
--- >>> modify fstL (*10) (3, "abc")
--- (30,"abc")
-fstL ::
-  Lens (a, x) (b, x) a b
-fstL =
-  error "todo: fstL"
-
--- |
---
--- >>> modify sndL (++ "def") (13, "abc")
--- (13,"abcdef")
-sndL ::
-  Lens (x, a) (x, b) a b
-sndL =
-  error "todo: sndL"
-
--- |
---
--- >>> get (mapL 3) (Map.fromList (map (\c -> (ord c - 96, c)) ['a'..'d']))
--- Just 'c'
---
--- >>> get (mapL 33) (Map.fromList (map (\c -> (ord c - 96, c)) ['a'..'d']))
--- Nothing
---
--- >>> set (mapL 3) (Map.fromList (map (\c -> (ord c - 96, c)) ['a'..'d'])) (Just 'X')
--- fromList [(1,'a'),(2,'b'),(3,'X'),(4,'d')]
---
--- >>> set (mapL 33) (Map.fromList (map (\c -> (ord c - 96, c)) ['a'..'d'])) (Just 'X')
--- fromList [(1,'a'),(2,'b'),(3,'c'),(4,'d'),(33,'X')]
---
--- >>> set (mapL 3) (Map.fromList (map (\c -> (ord c - 96, c)) ['a'..'d'])) Nothing
--- fromList [(1,'a'),(2,'b'),(4,'d')]
---
--- >>> set (mapL 33) (Map.fromList (map (\c -> (ord c - 96, c)) ['a'..'d'])) Nothing
--- fromList [(1,'a'),(2,'b'),(3,'c'),(4,'d')]
-mapL ::
-  Ord k =>
-  k
-  -> Lens (Map k v) (Map k v) (Maybe v) (Maybe v)
-mapL =
-  error "todo: mapL"
-
--- |
---
--- >>> get (setL 3) (Set.fromList [1..5])
--- True
---
--- >>> get (setL 33) (Set.fromList [1..5])
--- False
---
--- >>> set (setL 3) (Set.fromList [1..5]) True
--- fromList [1,2,3,4,5]
---
--- >>> set (setL 3) (Set.fromList [1..5]) False
--- fromList [1,2,4,5]
---
--- >>> set (setL 33) (Set.fromList [1..5]) True
--- fromList [1,2,3,4,5,33]
---
--- >>> set (setL 33) (Set.fromList [1..5]) False
--- fromList [1,2,3,4,5]
-setL ::
-  Ord k =>
-  k
-  -> Lens (Set.Set k) (Set.Set k) Bool Bool
-setL =
-  error "todo: setL"
-
--- |
---
--- >>> get (compose fstL sndL) ("abc", (7, "def"))
--- 7
---
--- >>> set (compose fstL sndL) ("abc", (7, "def")) 8
--- ("abc",(8,"def"))
-compose ::
-  Lens s t a b
-  -> Lens q r s t
-  -> Lens q r a b
-compose =
-  error "todo: compose"
-
--- | An alias for @compose@.
-(|.) ::
-  Lens s t a b
-  -> Lens q r s t
-  -> Lens q r a b
-(|.) =
-  compose
-
-infixr 9 |.
-
--- |
---
--- >>> get identity 3
--- 3
---
--- >>> set identity 3 4
--- 4
-identity ::
-  Lens a b a b
-identity =
-  error "todo: identity"
-
--- |
---
--- >>> get (product fstL sndL) (("abc", 3), (4, "def"))
--- ("abc","def")
---
--- >>> set (product fstL sndL) (("abc", 3), (4, "def")) ("ghi", "jkl")
--- (("ghi",3),(4,"jkl"))
-product ::
-  Lens s t a b
-  -> Lens q r c d
-  -> Lens (s, q) (t, r) (a, c) (b, d)
-product =
-  error "todo: product"
-
--- | An alias for @product@.
-(***) ::
-  Lens s t a b
-  -> Lens q r c d
-  -> Lens (s, q) (t, r) (a, c) (b, d)
-(***) =
-  product
-
-infixr 3 ***
-
--- |
---
--- >>> get (choice fstL sndL) (Left ("abc", 7))
--- "abc"
---
--- >>> get (choice fstL sndL) (Right ("abc", 7))
--- 7
---
--- >>> set (choice fstL sndL) (Left ("abc", 7)) "def"
--- Left ("def",7)
---
--- >>> set (choice fstL sndL) (Right ("abc", 7)) 8
--- Right ("abc",8)
-choice ::
-  Lens s t a b
-  -> Lens q r a b
-  -> Lens (Either s q) (Either t r) a b
-choice =
-  error "todo: choice"
-
--- | An alias for @choice@.
-(|||) ::
-  Lens s t a b
-  -> Lens q r a b
-  -> Lens (Either s q) (Either t r) a b
-(|||) =
-  choice
-
-infixr 2 |||
-
-----
-
-type Lens' a b =
-  Lens a a b b
-
-cityL ::
-  Lens' Locality String
-cityL p (Locality c t y) =
-  fmap (\c' -> Locality c' t y) (p c)
-
-stateL ::
-  Lens' Locality String
-stateL p (Locality c t y) =
-  fmap (\t' -> Locality c t' y) (p t)
-
-countryL ::
-  Lens' Locality String
-countryL p (Locality c t y) =
-  fmap (\y' -> Locality c t y') (p y)
-
-streetL ::
-  Lens' Address String
-streetL p (Address t s l) =
-  fmap (\t' -> Address t' s l) (p t)
-
-suburbL ::
-  Lens' Address String
-suburbL p (Address t s l) =
-  fmap (\s' -> Address t s' l) (p s)
-
-localityL ::
-  Lens' Address Locality
-localityL p (Address t s l) =
-  fmap (\l' -> Address t s l') (p l)
-
-ageL ::
-  Lens' Person Int
-ageL p (Person a n d) =
-  fmap (\a' -> Person a' n d) (p a)
-
-nameL ::
-  Lens' Person String
-nameL p (Person a n d) =
-  fmap (\n' -> Person a n' d) (p n)
-
-addressL ::
-  Lens' Person Address
-addressL p (Person a n d) =
-  fmap (\d' -> Person a n d') (p d)
-
-intAndIntL ::
-  Lens' (IntAnd a) Int
-intAndIntL p (IntAnd n a) =
-  fmap (\n' -> IntAnd n' a) (p n)
-
--- lens for polymorphic update
-intAndL ::
-  Lens (IntAnd a) (IntAnd b) a b
-intAndL p (IntAnd n a) =
-  fmap (\a' -> IntAnd n a') (p a)
-
--- |
---
--- >>> get (suburbL |. addressL) fred
--- "Fredville"
---
--- >>> get (suburbL |. addressL) mary
--- "Maryland"
-getSuburb ::
-  Person
-  -> String
-getSuburb =
-  error "todo: getSuburb"
-
--- |
---
--- >>> setStreet fred "Some Other St"
--- Person 24 "Fred" (Address "Some Other St" "Fredville" (Locality "Fredmania" "New South Fred" "Fredalia"))
---
--- >>> setStreet mary "Some Other St"
--- Person 28 "Mary" (Address "Some Other St" "Maryland" (Locality "Mary Mary" "Western Mary" "Maristan"))
-setStreet ::
-  Person
-  -> String
-  -> Person
-setStreet =
-  error "todo: setStreet"
-
--- |
---
--- >>> getAgeAndCountry (fred, maryLocality)
--- (24,"Maristan")
---
--- >>> getAgeAndCountry (mary, fredLocality)
--- (28,"Fredalia")
-getAgeAndCountry ::
-  (Person, Locality)
-  -> (Int, String)
-getAgeAndCountry =
-  error "todo: getAgeAndCountry"
-
--- |
---
--- >>> setCityAndLocality (fred, maryAddress) ("Some Other City", fredLocality)
--- (Person 24 "Fred" (Address "15 Fred St" "Fredville" (Locality "Some Other City" "New South Fred" "Fredalia")),Address "83 Mary Ln" "Maryland" (Locality "Fredmania" "New South Fred" "Fredalia"))
---
--- >>> setCityAndLocality (mary, fredAddress) ("Some Other City", maryLocality)
--- (Person 28 "Mary" (Address "83 Mary Ln" "Maryland" (Locality "Some Other City" "Western Mary" "Maristan")),Address "15 Fred St" "Fredville" (Locality "Mary Mary" "Western Mary" "Maristan"))
-setCityAndLocality ::
-  (Person, Address) -> (String, Locality) -> (Person, Address)
-setCityAndLocality =
-  error "todo: setCityAndLocality"
-  
--- |
---
--- >>> getSuburbOrCity (Left maryAddress)
--- "Maryland"
---
--- >>> getSuburbOrCity (Right fredLocality)
--- "Fredmania"
-getSuburbOrCity ::
-  Either Address Locality
-  -> String
-getSuburbOrCity =
-  error "todo: getSuburbOrCity"
-
--- |
---
--- >>> setStreetOrState (Right maryLocality) "Some Other State"
--- Right (Locality "Mary Mary" "Some Other State" "Maristan")
---
--- >>> setStreetOrState (Left fred) "Some Other St"
--- Left (Person 24 "Fred" (Address "Some Other St" "Fredville" (Locality "Fredmania" "New South Fred" "Fredalia")))
-setStreetOrState ::
-  Either Person Locality
-  -> String
-  -> Either Person Locality
-setStreetOrState =
-  error "todo: setStreetOrState"
-
--- |
---
--- >>> modifyCityUppercase fred
--- Person 24 "Fred" (Address "15 Fred St" "Fredville" (Locality "FREDMANIA" "New South Fred" "Fredalia"))
---
--- >>> modifyCityUppercase mary
--- Person 28 "Mary" (Address "83 Mary Ln" "Maryland" (Locality "MARY MARY" "Western Mary" "Maristan"))
-modifyCityUppercase ::
-  Person
-  -> Person
-modifyCityUppercase =
-  error "todo: modifyCityUppercase"
-
--- |
---
--- >>> modifyIntAndLengthEven (IntAnd 10 "abc")
--- IntAnd 10 False
---
--- >>> modifyIntAndLengthEven (IntAnd 10 "abcd")
--- IntAnd 10 True
-modifyIntAndLengthEven ::
-  IntAnd [a]
-  -> IntAnd Bool
-modifyIntAndLengthEven =
-  error "todo: modifyIntAndLengthEven"
-
-----
-
--- |
---
--- >>> over traverseLocality (map toUpper) (Locality "abc" "def" "ghi")
--- Locality "ABC" "DEF" "GHI"
-traverseLocality ::
-  Traversal' Locality String
-traverseLocality =
-  error "todo: traverseLocality"
-
--- |
---
--- >>> over intOrIntP (*10) (IntOrIs 3)
--- IntOrIs 30
---
--- >>> over intOrIntP (*10) (IntOrIsNot "abc")
--- IntOrIsNot "abc"
-intOrIntP ::
-  Prism' (IntOr a) Int
-intOrIntP =
-  error "todo: intOrIntP"
-
-intOrP ::
-  Prism (IntOr a) (IntOr b) a b
-intOrP =
-  error "todo: intOrP"
-
--- |
---
--- >> over intOrP (even . length) (IntOrIsNot "abc")
--- IntOrIsNot False
---
--- >>> over intOrP (even . length) (IntOrIsNot "abcd")
--- IntOrIsNot True
---
--- >>> over intOrP (even . length) (IntOrIs 10)
--- IntOrIs 10
-intOrLengthEven ::
-  IntOr [a]
-  -> IntOr Bool
-intOrLengthEven =
-  error "todo: intOrLengthEven"
diff --git a/src/Lets/Lens/Profunctor.hs b/src/Lets/Profunctor.hs
similarity index 93%
rename from src/Lets/Lens/Profunctor.hs
rename to src/Lets/Profunctor.hs
index 7c1acb0..92a3ddb 100644
--- a/src/Lets/Lens/Profunctor.hs
+++ b/src/Lets/Profunctor.hs
@@ -1,4 +1,4 @@
-module Lets.Lens.Profunctor (
+module Lets.Profunctor (
   Profunctor(dimap)
 ) where