diff --git a/Costack.hs b/Costack.hs
--- a/Costack.hs
+++ b/Costack.hs
@@ -11,7 +11,7 @@
   Costack.sort, Costack.strictSort, Costack.sorted, Costack.strictSorted,
 ) where ---------------------------------------------------------------------------------------------------------------
 
-  import qualified List as L
+  import qualified Data.List as L
 
   data Costack a = COSTACK [a]
     deriving (Show, Read, Eq)
diff --git a/DefaultPropLogic.hs b/DefaultPropLogic.hs
--- a/DefaultPropLogic.hs
+++ b/DefaultPropLogic.hs
@@ -901,7 +901,7 @@
 
 -- import
 
-  import qualified List        as L
+  import qualified Data.List   as L
   import qualified Olist       as O
   import qualified TextDisplay as D
   import PropLogicCore
diff --git a/FastPropLogic.hs b/FastPropLogic.hs
--- a/FastPropLogic.hs
+++ b/FastPropLogic.hs
@@ -268,7 +268,7 @@
 
 -- import
 
-  import qualified List        as L
+  import qualified Data.List   as L
   import qualified TextDisplay as D
   import qualified Olist       as O
   import qualified Costack     as C
diff --git a/Main.hs b/Main.hs
--- a/Main.hs
+++ b/Main.hs
@@ -8,7 +8,7 @@
 
 -- imports
 
-  import System (getArgs)
+  import System.Environment (getArgs)
   import qualified TextDisplay as D
   import qualified Costack as C
   import PropLogic
diff --git a/PropLogic.cabal b/PropLogic.cabal
--- a/PropLogic.cabal
+++ b/PropLogic.cabal
@@ -1,5 +1,5 @@
 Name:           PropLogic
-Version:        0.9
+Version:        0.9.0.1
 Cabal-Version:  >= 1.2
 Build-type:     Simple
 License:        BSD3
@@ -21,7 +21,7 @@
   other-modules:
     TextDisplay, Costack
   build-depends:
-    base < 5, haskell98
+    base < 5, old-time, random
   extensions:
     TypeSynonymInstances, FlexibleInstances, MultiParamTypeClasses
 
diff --git a/PropLogicCore.hs b/PropLogicCore.hs
--- a/PropLogicCore.hs
+++ b/PropLogicCore.hs
@@ -97,7 +97,7 @@
 
 -- imports
 
-  import qualified List        as L
+  import qualified Data.List   as L
   import qualified TextDisplay as D
   import qualified Olist       as O
 
diff --git a/PropLogicTest.hs b/PropLogicTest.hs
--- a/PropLogicTest.hs
+++ b/PropLogicTest.hs
@@ -244,12 +244,12 @@
 
 ) where ---------------------------------------------------------------------------------------------------------------
 
-  import Char (chr)
-  import Ratio
-  import Random (randomIO, randomRIO)
+  import Data.Char (chr)
+  import Data.Ratio
+  import System.Random (randomIO, randomRIO)
   import Control.Monad
-  import CPUTime (getCPUTime)
-  import qualified Time  as T
+  import System.CPUTime (getCPUTime)
+  import qualified System.Time  as T
   import qualified Olist as O
   import qualified TextDisplay as D
   import qualified Costack as C
diff --git a/TextDisplay.hs b/TextDisplay.hs
--- a/TextDisplay.hs
+++ b/TextDisplay.hs
@@ -157,8 +157,8 @@
 
 -- import
 
-  import qualified Char as Ch
-  import qualified List as L
+  import qualified Data.Char as Ch
+  import qualified Data.List as L
 
 -- basic definitions and basic functions