diff --git a/CHANGELOG.md b/CHANGELOG.md
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,9 @@
 # recursion
 
+## 2.2.4.4
+
+* Augment documentation
+
 ## 2.2.4.3
 
 * Fix documentation
diff --git a/recursion.cabal b/recursion.cabal
--- a/recursion.cabal
+++ b/recursion.cabal
@@ -1,6 +1,6 @@
 cabal-version:      1.18
 name:               recursion
-version:            2.2.4.3
+version:            2.2.4.4
 license:            BSD3
 license-file:       LICENSE
 copyright:          Copyright: (c) 2018-2020 Vanessa McHale
@@ -35,16 +35,16 @@
     hs-source-dirs:   src
     default-language: Haskell2010
     other-extensions:
-        DeriveFunctor FlexibleContexts ExistentialQuantification RankNTypes
+        DeriveFunctor FlexibleContexts ExistentialQuantification Rank2Types
         TypeFamilies DeriveFoldable DeriveTraversable DefaultSignatures
         TypeOperators MultiParamTypeClasses
 
     ghc-options:      -Wall
     build-depends:
         base >=4.9 && <5,
-        composition-prelude -any
+        composition-prelude
 
-    if impl(eta -any)
+    if impl(eta >=0)
         buildable: False
 
     if (flag(development) && !impl(ghc >=8.8))
diff --git a/src/Control/Recursion.hs b/src/Control/Recursion.hs
--- a/src/Control/Recursion.hs
+++ b/src/Control/Recursion.hs
@@ -5,7 +5,7 @@
 {-# LANGUAGE ExistentialQuantification #-}
 {-# LANGUAGE FlexibleContexts          #-}
 {-# LANGUAGE MultiParamTypeClasses     #-}
-{-# LANGUAGE RankNTypes                #-}
+{-# LANGUAGE Rank2Types                #-}
 {-# LANGUAGE TypeFamilies              #-}
 {-# LANGUAGE TypeOperators             #-}
 
@@ -312,8 +312,26 @@
 --
 -- >>> spongebobZygo "Hello, World"
 -- "HeLlO, wOrLd"
+--
+-- >>> :set -XFlexibleContexts
+-- >>> :{
+-- let {
+--   succDiff :: Integral a => [a] -> [a] ;
+--   succDiff = zygo a pa
+--       where a Nil = Nothing
+--             a (Cons i _) = Just i
+--             pa Nil = []
+--             pa (Cons x (Nothing, xs)) = []
+--             pa (Cons x (Just y, xs)) = (y - x) : xs
+-- }
+-- :}
+--
+-- >>> succDiff [ i^2 | i <- [1..10] ]
+-- [3,5,7,9,11,13,15,17,19]
 zygo :: (Recursive t) => (Base t b -> b) -> (Base t (b, a) -> a) -> t -> a
 zygo f g = snd . cata (\x -> (f (fmap fst x), g x))
+
+-- todo: successive difference?
 
 -- | Paramorphism
 --
diff --git a/src/Control/Recursion/GHC.hs b/src/Control/Recursion/GHC.hs
--- a/src/Control/Recursion/GHC.hs
+++ b/src/Control/Recursion/GHC.hs
@@ -1,4 +1,4 @@
-{-# LANGUAGE RankNTypes #-}
+{-# LANGUAGE Rank2Types #-}
 
 -- | This module contains GHC-specific functions
 module Control.Recursion.GHC ( transverse