diff --git a/CHANGELOG.md b/CHANGELOG.md
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -15,3 +15,7 @@
 ## 0.1.3.0 -- 2020-05-13
 
 * added chronoM, cochronoM and the variants.
+
+## 0.1.3.1 -- 2020-05-13
+
+* added comment
diff --git a/monadic-recursion-schemes.cabal b/monadic-recursion-schemes.cabal
--- a/monadic-recursion-schemes.cabal
+++ b/monadic-recursion-schemes.cabal
@@ -4,7 +4,7 @@
 -- http://haskell.org/cabal/users-guide/
 
 name:                monadic-recursion-schemes
-version:             0.1.3.0
+version:             0.1.3.1
 synopsis:            Recursion Schemes for Monadic version.
 description:         Yet another recursion schemes for monadic style, depends on recursion-schemes.
 homepage:            https://github.com/cutsea110/monadic-recursion-schemes.git
diff --git a/src/Data/Functor/Foldable/Monadic.hs b/src/Data/Functor/Foldable/Monadic.hs
--- a/src/Data/Functor/Foldable/Monadic.hs
+++ b/src/Data/Functor/Foldable/Monadic.hs
@@ -155,7 +155,7 @@
 chronoM phi psi = histoM phi <=< futuM psi
 
 cochronoM :: (Monad m, Corecursive c, Traversable (Base c), Traversable (Base t), Recursive t)
-          => (Base t (Cofree (Base t) a) -> m a)
-          -> (a -> m (Base c (Free (Base c) a)))
+          => (Base t (Cofree (Base t) a) -> m a) -- ^ algebra
+          -> (a -> m (Base c (Free (Base c) a))) -- ^ coalgebra
           -> t -> m c
 cochronoM phi psi = futuM psi <=< histoM phi