diff --git a/ChangeLog.md b/ChangeLog.md
--- a/ChangeLog.md
+++ b/ChangeLog.md
@@ -49,3 +49,7 @@
 ## 0.8.1.0 -- 2020-07-31
 
 * Eigth version revised A. Fixed issue with being not compiled fo GHC versions prior to 8.4* series. 
+
+## 0.9.0.0 -- 2020-08-01
+
+* Ninth version. Fixed issues with empty lists in the norms for some variants in DobutokO.Poetry.Norms module. Some documentation improvements.
diff --git a/DobutokO/Poetry/Norms.hs b/DobutokO/Poetry/Norms.hs
--- a/DobutokO/Poetry/Norms.hs
+++ b/DobutokO/Poetry/Norms.hs
@@ -49,6 +49,7 @@
 norm4 :: [Int] -> Int
 norm4 xs 
  | null xs = 0
+ | length xs == 1 = head xs
  | otherwise = maximum xs + sum xs + maximum (xs \\ [maximum xs])
 {-# INLINE norm4 #-} 
 
@@ -56,6 +57,7 @@
 norm5 :: [Int] -> Int
 norm5 xs 
  | null xs = 0
+ | length xs == 1 = head xs
  | minimum xs == 0 = norm5 . filter (/= 0) $ xs
  | otherwise = sum xs `quot` (minimum xs + minimum (xs \\ [minimum xs]))
 {-# INLINE norm5 #-} 
@@ -64,7 +66,12 @@
 norm51 :: [Int] -> Int
 norm51 xs 
  | null xs = 0
- | compare (minimum xs) 1 /= GT = let ys = filter (\t -> compare t 1 == GT) xs in (3 * sum xs) `quot` (minimum ys + minimum (ys \\ [minimum ys]))
+ | compare (minimum xs) 1 /= GT = let ys = filter (\t -> compare t 1 == GT) xs in 
+    case length ys of
+      0 -> sum xs
+      1 -> (3 * sum xs) `quot` (minimum ys + maximum ys)
+      _ -> (3 * sum xs) `quot` (minimum ys + minimum (ys \\ [minimum ys]))
+ | length xs == 1 = (3 * sum xs) `quot` (minimum xs + maximum xs)
  | otherwise = (3 * sum xs) `quot` (minimum xs + minimum (xs \\ [minimum xs]))
 {-# INLINE norm51 #-} 
 
@@ -74,10 +81,19 @@
 norm513 xs 
  | null xs = 0
  | compare (minimum xs) 1 /= GT = 
-   let ys = filter (\t -> compare t 1 == GT) xs 
-       zs = ys \\ [minimum ys] in (3 * sum xs) `quot` (minimum ys + minimum zs + minimum (zs \\ [minimum zs]))
+   let ys = filter (\t -> compare t 1 == GT) xs in 
+     case length ys of 
+       0 -> sum xs
+       1 -> (3 * sum xs) `quot` (minimum ys + maximum ys)
+       2 -> let zs = ys \\ [minimum ys] in (3 * sum xs) `quot` (minimum ys + 2 * minimum zs)
+       _ -> let zs = ys \\ [minimum ys] in (3 * sum xs) `quot` (minimum ys + minimum zs + minimum (zs \\ [minimum zs]))
  | otherwise = 
-   let zs = xs \\ [minimum xs] in (3 * sum xs) `quot` (minimum xs + minimum zs + minimum (zs \\ [minimum zs]))
+   let zs = xs \\ [minimum xs] in 
+     case length zs of 
+       0 -> sum xs
+       1 -> (3 * sum xs) `quot` (minimum zs + maximum zs)
+       2 -> let ts = zs \\ [minimum zs] in (3 * sum xs) `quot` (minimum zs + 2 * minimum ts)
+       _ -> let ts = zs \\ [minimum zs] in (3 * sum xs) `quot` (minimum zs + minimum ts + minimum (ts \\ [minimum ts]))
 {-# INLINE norm513 #-}   
 
 -- | The sixth norm for the list of non-negative 'Int'.
diff --git a/DobutokO/Poetry/StrictV.hs b/DobutokO/Poetry/StrictV.hs
--- a/DobutokO/Poetry/StrictV.hs
+++ b/DobutokO/Poetry/StrictV.hs
@@ -6,8 +6,7 @@
 -- Maintainer  :  olexandr543@yahoo.com
 --
 -- Helps to order the 7 or less Ukrainian words (or their concatenations) 
--- to obtain (to some extent) suitable for poetry or music text. The main 
--- module in the library that imports all other ones except Main.
+-- to obtain (to some extent) suitable for poetry or music text. 
 
 {-# LANGUAGE CPP, BangPatterns #-}
 
diff --git a/dobutokO-poetry.cabal b/dobutokO-poetry.cabal
--- a/dobutokO-poetry.cabal
+++ b/dobutokO-poetry.cabal
@@ -2,7 +2,7 @@
 -- documentation, see http://haskell.org/cabal/users-guide/
 
 name:                dobutokO-poetry
-version:             0.8.1.0
+version:             0.9.0.0
 synopsis:            Helps to order the 7 or less Ukrainian words to obtain somewhat suitable for poetry or music text
 description:         Helps to order the 7 or less Ukrainian words (or their concatenations) to obtain somewhat suitable for poetry or music text. Can be also used as a research instrument with generalized functions.