diff --git a/ac-library-hs.cabal b/ac-library-hs.cabal
--- a/ac-library-hs.cabal
+++ b/ac-library-hs.cabal
@@ -3,7 +3,7 @@
 -- PVP summary:  +-+------- breaking API changes
 --               | | +----- non-breaking API additions
 --               | | | +--- code changes with no API change
-version: 1.5.3.1
+version: 1.5.3.2
 synopsis: Data structures and algorithms
 description:
   Haskell port of [ac-library](https://github.com/atcoder/ac-library), a library for competitive
diff --git a/src/AtCoder/FenwickTree.hs b/src/AtCoder/FenwickTree.hs
--- a/src/AtCoder/FenwickTree.hs
+++ b/src/AtCoder/FenwickTree.hs
@@ -31,6 +31,11 @@
 -- >>> FT.sum ft 0 3
 -- 8
 --
+-- ==== Known bugs
+--
+-- Currently, `maxRight` and `maxRightM` are not reliable. If you need it, please use `SegTree`
+-- instead.
+--
 -- @since 1.0.0.0
 module AtCoder.FenwickTree
   ( -- * Fenwick tree
@@ -140,7 +145,9 @@
 sumMaybe :: (HasCallStack, PrimMonad m, Num a, VU.Unbox a) => FenwickTree (PrimState m) a -> Int -> Int -> m (Maybe a)
 sumMaybe ft l r = stToPrim $ sumMaybeST ft l r
 
--- | (Extra API) Applies a binary search on the Fenwick tree. It returns an index \(r\) that
+-- | known bugs: this function is not reliable. if you need t, please use `segtree` instead.
+--
+-- (Extra API) Applies a binary search on the Fenwick tree. It returns an index \(r\) that
 -- satisfies both of the following.
 --
 -- - \(r = l\) or \(f(a[l] + a[l + 1] + ... + a[r - 1])\) returns `True`.
@@ -171,7 +178,9 @@
   m Int
 maxRight ft l0 f = maxRightM ft l0 (pure . f)
 
--- | (Extra API) Monadic variant of `maxRight`.
+-- | known bugs: this function is not reliable. if you need t, please use `segtree` instead.
+--
+-- (Extra API) Monadic variant of `maxRight`.
 --
 -- ==== Constraints
 -- - if \(f\) is called with the same argument, it returns the same value, i.e., \(f\) has no side effect.
diff --git a/src/AtCoder/LazySegTree.hs b/src/AtCoder/LazySegTree.hs
--- a/src/AtCoder/LazySegTree.hs
+++ b/src/AtCoder/LazySegTree.hs
@@ -14,10 +14,14 @@
 -- - Acting the map \(f\in F\) (cf. \(x = f(x)\)) on all the elements of an interval
 -- - Calculating the product of the elements of an interval
 --
--- In Haskell types, \(F\) is a `SegAct` (@'segAct' f@) and \(S\) is a `Monoid`. For simplicity, in
--- this document, we assume that the relevant methods work in constant time. If these work in
--- \(O(T)\) time, each time complexity appear in this document is multiplied by \(O(T)\).
+-- In Haskell types, \(F\) is a `SegAct` (@'segAct' f@) and \(S\) is a `Monoid`. You would want to
+-- look into @AtCoder.Extra.Monoid@ for builtin monoid action types. For example, there's no
+-- implementation of @SegAct (Sum Int) (Sum Int)@, but you have @SegAct (RangeAdd Int) (Sum Int)@.
 --
+-- For simplicity, in this document, we assume that the relevant methods work in constant time. If
+-- these work in \(O(T)\) time, each time complexity appear in this document is multiplied by
+-- \(O(T)\).
+--
 -- ==== __Example__
 -- Here we'll use `AtCoder.Extra.Monoid.Affine1` as a monoid action \(F\) and `Data.Semigroup.Sum`
 -- as the acted monoid \(S\):
@@ -66,6 +70,7 @@
 --
 -- ==== Tips
 --
+-- - See @AtCoder.Extra.Monoid@ for builtin monoid action types.
 -- - `prod` returns \(a_l \cdot a_{l + 1} \cdot .. \cdot a_{r - 1}\). If you need \(a_{r - 1} \cdot a_{r - 2} \cdot .. \cdot a_{l}\),
 -- wrap your monoid in `Data.Monoid.Dual`.
 -- - If you ever need to store boxed types to `LazySegTree`, wrap it in @Data.Vector.Unboxed.DoNotUnboxStrict@
@@ -133,7 +138,7 @@
 import Prelude hiding (read)
 
 -- | Typeclass reprentation of the `LazySegTree` properties. User can implement either `segAct` or
--- `segActWithLength`.
+-- `segActWithLength`. See @AtCoder.Extra.Monoid@ for builtin monoid action types.
 --
 -- Instances should satisfy the follwing properties:
 --
@@ -150,7 +155,7 @@
 -- order is important for non-commutative monoid implementations.
 --
 -- ==== __Example instance__
--- Take `AtCoder.Extra.Monoid.Affine1` as an example of type \(F\).
+-- Take `AtCoder.Extra.Monoid.Affine1` as an example of type \(F\) instance.
 --
 -- @
 -- {-# LANGUAGE TypeFamilies #-}