diff --git a/README.md b/README.md
--- a/README.md
+++ b/README.md
@@ -2,32 +2,79 @@
 
 Haskell Hall Symbols Library
 
-# Quickstart
+## Quickstart
 
+Make new stack project and move to project directory.
+
 ```shell
+% stack new hmRepl
+% cd hmRepl
+```
+
+Edit extra-deps part of stack.yaml like below.
+
+```
+extra-deps:
+- matrix-as-xyz-0.1.1.1
+- symmetry-operations-symbols-0.0.1.2
+- hall-symbols-0.1.0.4
+```
+
+Build project.
+
+```shell
+% stack build
+```
+
+Then start repl.
+
+```shell
 % stack repl
 ```
 
+Setup packages and load modules.
+
 ```haskell
--- prepare
 repl> :set -package matrix-as-xyz
-repl> :m Data.Matrix.AsXYZ
-repl> :l Crystallography.HallSymbols
+repl> :set -package symmetry-operations-symbols
+repl> :set -package hall-symbols
+repl> :m Data.Matrix.AsXYZ Data.Matrix.SymmetryOperationsSymbols Crystallography.HallSymbols
+```
 
--- print general positions
-repl> fmap prettyXYZ $ fromHallSymbols' "C -2yc"
+Use like below.
 
+```haskell
+-- print General Positions.
+repl> prettyXYZ <$> fromHallSymbols' "C -2yc"
  ["x,y,z","x+1/2,y+1/2,z","x,-y,z+1/2","x+1/2,-y+1/2,z+1/2"]
 
--- print generators
-repl> fmap prettyXYZ $ fromHallSymbols'' "C -2yc"
+repl> fromHallSymbols' "C -2yc" >>= fromMatrix'
+[" 1 "," c  x,0,z"," t (1/2,1/2,0) "," n (1/2,0,1/2) x,1/4,z"]
 
+```
+
+Or use like below.
+
+```haskell
+-- print Generators
+repl> prettyXYZ <$> generatorsOfHallSymbols "C -2yc"
 ["x,y,z","x+1/2,y+1/2,z","x,-y,z+1/2"]
+
+repl> generatorsOfHallSymbols "C -2yc" >>= fromMatrix'
+[" 1 "," t (1/2,1/2,0) "," c  x,0,z"]
+
 ```
 
+## References
 
+1. Concise Space-Group Symbols http://cci.lbl.gov/sginfo/hall_symbols.html , See also : https://github.com/rwgk/sginfo
 
+2. Space-Group Notation with an Explicit Origin
+   S.R. Hall; Space-Group Notation with an Explicit Origin ; Acta Cryst. (1981). A37, 517-525
+
+3. ITVB 2001 Table A1.4.2.7 Hall symbols http://cci.lbl.gov/sginfo/itvb_2001_table_a1427_hall_symbols.html
+
 ## License
 
-See the [LICENSE](LICENSE)
+See the [LICENSE](https://raw.githubusercontent.com/narumij/hall-symbols/master/LICENSE)
 file in the repository.
diff --git a/hall-symbols.cabal b/hall-symbols.cabal
--- a/hall-symbols.cabal
+++ b/hall-symbols.cabal
@@ -4,10 +4,10 @@
 --
 -- see: https://github.com/sol/hpack
 --
--- hash: 702da6b77b983eb8b29d4431755b69ea93d2ecadc33590f79090f8406752c85a
+-- hash: c2e2ed9f27fb5a7cf649dcd9c0d306d1fa2de8b0760efccb8a138d070cbf0d12
 
 name:           hall-symbols
-version:        0.1.0.3
+version:        0.1.0.4
 synopsis:       Symmetry operations generater of Hall Symbols
 description:    Please see the README on GitHub at <https://github.com/narumij/hall-symbols#readme>
 category:       Chemistry
diff --git a/src/Crystallography/HallSymbols.hs b/src/Crystallography/HallSymbols.hs
--- a/src/Crystallography/HallSymbols.hs
+++ b/src/Crystallography/HallSymbols.hs
@@ -22,9 +22,11 @@
 module Crystallography.HallSymbols (
   fromHallSymbols,
   fromHallSymbols',
+  generatorsOfHallSymbols,
   hallSymbols,
 --  hallSymbols',
   parser,
+  generators,
   LatticeSymbol,
   MatrixSymbol,
   OriginShift,
@@ -179,8 +181,8 @@
   Right mm -> mm
 
 -- | Generate Generators by 4x4 matrix (unsafe version)
-fromHallSymbols'' :: String -> [Matrix Rational]
-fromHallSymbols'' s = case gg s of
+generatorsOfHallSymbols :: String -> [Matrix Rational]
+generatorsOfHallSymbols s = case gg s of
   Left e -> error $ show e
   Right mm -> mm
   where
diff --git a/src/Crystallography/HallSymbols/SpacegroupSymbols.hs b/src/Crystallography/HallSymbols/SpacegroupSymbols.hs
--- a/src/Crystallography/HallSymbols/SpacegroupSymbols.hs
+++ b/src/Crystallography/HallSymbols/SpacegroupSymbols.hs
@@ -396,7 +396,7 @@
   (  "88:1",  "I 41/a:1",  "I 4bw -1bw"  ),
   (  "88:2",  "I 41/a:2",  "-I 4ad"  ),
   (  "89",  "P 4 2 2",  "P 4 2"  ),
-  (  "90",  "P 4 21 2",  "P 4ab 2ab"  ),
+  (  "90",  "P 42 1 2",  "P 4ab 2ab"  ),
   (  "91",  "P 41 2 2",  "P 4w 2c"  ),
   (  "92",  "P 41 21 2",  "P 4abw 2nw"  ),
   (  "93",  "P 42 2 2",  "P 4c 2"  ),