diff --git a/Examples/fibs.hs b/Examples/fibs.hs
new file mode 100644
--- /dev/null
+++ b/Examples/fibs.hs
@@ -0,0 +1,34 @@
+{-# LANGUAGE OverloadedStrings #-}
+
+import Text.LaTeX.Base.Monad
+
+main :: IO ()
+main = execLaTeXT example >>= renderFile "Fibs.tex"
+
+example :: Monad m => LaTeXT_ m
+example = do
+ documentclass [] article
+ document exampleBody
+
+exampleBody :: Monad m => LaTeXT_ m
+exampleBody = do
+ "This is an example of how "
+ hatex3
+ " works, printing a table of "
+ "the thirteen first elements of the "
+ "Fibonacci sequence."
+ bigskip
+ center $ underline $ textbf "Fibonacci table"
+ center $ tabular Nothing [RightColumn,VerticalLine,LeftColumn] $ do
+   textbf "Fibonacci number" & textbf "Value"
+   lnbk
+   hline
+   foldr (\n l -> do fromString (show n) & fromString (show $ fib n)
+                     lnbk
+                     l ) (return ()) [0..12]
+
+fibs :: [Int]
+fibs = 1 : 1 : zipWith (+) fibs (tail fibs)
+
+fib :: Int -> Int
+fib = (fibs!!)
diff --git a/HaTeX.cabal b/HaTeX.cabal
--- a/HaTeX.cabal
+++ b/HaTeX.cabal
@@ -1,11 +1,11 @@
 Name: HaTeX
-Version: 3.0.0
+Version: 3.1.0
 Author: Daniel Díaz
 Category: Text
 Build-type: Simple
 License: BSD3
 License-file: license
-Maintainer: Daniel Díaz {danieldiaz <at> dhelta <dot> net}
+Maintainer: Daniel Díaz (danieldiaz <at> dhelta <dot> net)
 Stability: Experimental
 Homepage: http://dhelta.net/hprojects/HaTeX
 Bug-reports: danieldiaz <at> dhelta <dot> net
@@ -17,13 +17,17 @@
              for any purpose you can figure out.
 Cabal-version: >= 1.6
 Tested-with: GHC == 6.12.3 , GHC == 7.0.3
-Extra-source-files: ReleaseNotes
+Extra-source-files:
+  ReleaseNotes
+  -- Examples
+  Examples/fibs.hs
 
 Library
   Build-depends: base ==4.*
                , bytestring
                , mtl ==2.*
-               , text
+               , text
+  GHC-Options: -fno-warn-unrecognised-pragmas
   Exposed-modules:
     Text.LaTeX
       Text.LaTeX.Monad
@@ -36,12 +40,15 @@
         Text.LaTeX.Base.Syntax
         Text.LaTeX.Base.Types
         Text.LaTeX.Base.Writer
+        Text.LaTeX.Base.Warnings
       Text.LaTeX.Packages
         Text.LaTeX.Packages.Monad
         Text.LaTeX.Packages.AMSFonts
           Text.LaTeX.Packages.AMSFonts.Monad
         Text.LaTeX.Packages.AMSMath
           Text.LaTeX.Packages.AMSMath.Monad
+        Text.LaTeX.Packages.AMSThm
+          Text.LaTeX.Packages.AMSThm.Monad
         Text.LaTeX.Packages.Beamer
           Text.LaTeX.Packages.Beamer.Monad
         Text.LaTeX.Packages.Hyperref
diff --git a/ReleaseNotes b/ReleaseNotes
--- a/ReleaseNotes
+++ b/ReleaseNotes
@@ -1,5 +1,38 @@
 HaTeX Release Notes
 -- From version 3.0.0
+
+>>> 3.1.0
+
+Highlights:
+
++ Added warnings (See Text.LaTeX.Base.Warnings).
++ Added an "Examples" directory.
++ Num instance for LaTeX and LaTeXT.
++ New package implemented "AMSThm" (See Text.LaTeX.Packages.AMSThm).
+
+Changes by modules:
+
+** Base modules
+* Text.LaTeX.Base.Syntax:
+-- Added Eq instance to LaTeX and TeXArg.
+* Text.LaTeX.Base.Writer:
+-- Added MonadTrans instance to LaTeXT.
+-- New functions: execLaTeXTWarn, liftFun, liftOp.
+* Text.LaTeX.Base.Types:
+-- Added Eq instance to Label.
+* Text.LaTeX.Base:
+-- Added Num instance to LaTeX.
+* Text.LaTeX.Base.Monad:
+-- Added Num instance to LaTeXT.
+* Text.LaTeX.Base.Commands:
+-- New function: between.
+
+** Package modules:
+* Text.LaTeX.Packages.AMSMath
+-- New symbols: (=:) , (/=:) , forall
+              , dagger, ddagger, in_ , ni
+              , (<:) , (<=:)
+              , (>:) , (>=:)
 
 >>> 3.0.0
 
diff --git a/Text/LaTeX.hs b/Text/LaTeX.hs
--- a/Text/LaTeX.hs
+++ b/Text/LaTeX.hs
@@ -3,7 +3,7 @@
 --   Importing this will you give access to almost all
 --   functionality of the library. It is recommended
 --   to import the @Base@ module and, then, import only
---   packages you will need.
+--   packages you actually need.
 module Text.LaTeX
  ( module Text.LaTeX.Base
  , module Text.LaTeX.Packages
diff --git a/Text/LaTeX/Base.hs b/Text/LaTeX/Base.hs
--- a/Text/LaTeX/Base.hs
+++ b/Text/LaTeX/Base.hs
@@ -14,6 +14,8 @@
 
 * The "Text.LaTeX.Base.Commands" module, which exports the LaTeX standard commands
   and environments.
+
+Here is also defined a 'Num' instance for 'LaTeX'.
 -}
 module Text.LaTeX.Base
  ( LaTeX , (<>)
@@ -22,7 +24,20 @@
  , module Text.LaTeX.Base.Commands
    ) where
 
-import Text.LaTeX.Base.Syntax (LaTeX,(<>))
+import Text.LaTeX.Base.Syntax (LaTeX (..),(<>))
 import Text.LaTeX.Base.Render
 import Text.LaTeX.Base.Types
 import Text.LaTeX.Base.Commands
+
+-- Num instance for LaTeX
+
+-- | Methods 'abs' and 'signum' are undefined. Don't use them!
+instance Num LaTeX where
+ (+) = TeXOp "+"
+ (-) = TeXOp "-"
+ (*) = (<>)
+ negate = (TeXEmpty -)
+ fromInteger = TeXRaw . fromString . show
+ -- Non-defined methods
+ abs _    = "Cannot use \"abs\" Num method with a LaTeX value."
+ signum _ = "Cannot use \"signum\" Num method with a LaTeX value."
diff --git a/Text/LaTeX/Base/Commands.hs b/Text/LaTeX/Base/Commands.hs
--- a/Text/LaTeX/Base/Commands.hs
+++ b/Text/LaTeX/Base/Commands.hs
@@ -1,8 +1,10 @@
 {-# LANGUAGE OverloadedStrings #-}
+{-# OPTIONS_HATEX MakeMonadic #-}
 
 -- | LaTeX standard commands and environments.
 module Text.LaTeX.Base.Commands
- ( raw
+ ( -- * Basic functions
+   raw , between
    -- * Preamble commands
  , title
  , author
@@ -154,10 +156,6 @@
  , roman_
  , alph
  , alph_
-   -- ** Cross references
- , label
- , ref
- , pageref
    -- ** Boxes
  , mbox
  , fbox
@@ -166,6 +164,10 @@
  , makebox
  , raisebox
  , rule
+   -- * Cross references
+ , label
+ , ref
+ , pageref
    -- ** Tables
  , tabular
  , (&)
@@ -191,6 +193,11 @@
 raw :: Text -> LaTeX
 raw = TeXRaw
 
+-- | Calling 'between' @c l1 l2@ puts @c@ between @l1@ and @l2@ and
+--   appends them.
+between :: LaTeX -> LaTeX -> LaTeX -> LaTeX
+between c l1 l2 = l1 <> c <> l2
+
 -- | Generate the title. It normally contains the 'title' name
 -- of your document, the 'author'(s) and 'date'.
 maketitle :: LaTeX
@@ -300,15 +307,6 @@
 cite :: LaTeX -> LaTeX
 cite l = TeXComm "cite" [FixArg l]
 
-ref :: Label -> LaTeX
-ref l = TeXComm "ref" [FixArg $ TeXRaw $ render l]
-
-label :: Label -> LaTeX
-label l = TeXComm "label" [FixArg $ TeXRaw $ render l]
-
-pageref :: Label -> LaTeX
-pageref l = TeXComm "pageref" [FixArg $ TeXRaw $ render l]
-
 documentclass :: [LaTeX] -> LaTeX -> LaTeX
 documentclass ls l = TeXComm "documentclass" [MOptArg ls , FixArg l]
 
@@ -727,4 +725,13 @@
 hatex_version :: LaTeX
 hatex_version = hatex3
              <> hspace (Ex $ negate 0.3)
-             <> emph ".0.0"
+             <> emph ".1.0"
+
+label :: Label -> LaTeX
+label l = TeXComm "label" [FixArg $ TeXRaw $ render l]
+
+ref :: Label -> LaTeX
+ref l = TeXComm "ref" [FixArg $ TeXRaw $ render l]
+
+pageref :: Label -> LaTeX
+pageref l = TeXComm "pageref" [FixArg $ TeXRaw $ render l]
diff --git a/Text/LaTeX/Base/Commands/Monad.hs b/Text/LaTeX/Base/Commands/Monad.hs
--- a/Text/LaTeX/Base/Commands/Monad.hs
+++ b/Text/LaTeX/Base/Commands/Monad.hs
@@ -9,7 +9,8 @@
 -- /and therefore, changes must to be done in these places./
 
 module Text.LaTeX.Base.Commands.Monad
- ( raw
+ ( -- * Basic functions
+   raw , between
    -- * Preamble commands
  , title
  , author
@@ -161,10 +162,6 @@
  , roman_
  , alph
  , alph_
-   -- ** Cross references
- , label
- , ref
- , pageref
    -- ** Boxes
  , mbox
  , fbox
@@ -173,6 +170,10 @@
  , makebox
  , raisebox
  , rule
+   -- * Cross references
+ , label
+ , ref
+ , pageref
    -- ** Tables
  , tabular
  , (&)
@@ -201,6 +202,17 @@
 raw a1 = do textell ( App.raw a1)
 
 {-|
+Calling 'between' @c l1 l2@ puts @c@ between @l1@ and @l2@ and
+   appends them.
+-}
+between ::   (Monad m) => LaTeXT_ m -> LaTeXT_ m -> LaTeXT_ m -> LaTeXT_ m
+between a1 a2 a3
+  = do a1 <- extractLaTeX_ a1
+       a2 <- extractLaTeX_ a2
+       a3 <- extractLaTeX_ a3
+       textell ( App.between a1 a2 a3)
+
+{-|
 Generate the title. It normally contains the 'title' name
  of your document, the 'author'(s) and 'date'.
 -}
@@ -400,18 +412,6 @@
        textell ( App.cite a1)
 
 
-ref ::   (Monad m) => Label -> LaTeXT_ m
-ref a1 = do textell ( App.ref a1)
-
-
-label ::   (Monad m) => Label -> LaTeXT_ m
-label a1 = do textell ( App.label a1)
-
-
-pageref ::   (Monad m) => Label -> LaTeXT_ m
-pageref a1 = do textell ( App.pageref a1)
-
-
 documentclass ::   (Monad m) => [LaTeXT_ m] -> LaTeXT_ m -> LaTeXT_ m
 documentclass a1 a2
   = do a1 <- mapM extractLaTeX_ a1
@@ -1007,5 +1007,17 @@
 
 hatex_version ::   (Monad m) => LaTeXT_ m
 hatex_version = do textell ( App.hatex_version)
+
+
+label ::   (Monad m) => Label -> LaTeXT_ m
+label a1 = do textell ( App.label a1)
+
+
+ref ::   (Monad m) => Label -> LaTeXT_ m
+ref a1 = do textell ( App.ref a1)
+
+
+pageref ::   (Monad m) => Label -> LaTeXT_ m
+pageref a1 = do textell ( App.pageref a1)
 
 
diff --git a/Text/LaTeX/Base/Monad.hs b/Text/LaTeX/Base/Monad.hs
--- a/Text/LaTeX/Base/Monad.hs
+++ b/Text/LaTeX/Base/Monad.hs
@@ -17,6 +17,8 @@
 
 * The "Text.LaTeX.Base.Commands.Monad" module, which exports the LaTeX standard commands
   and environments.
+
+Here is also defined a 'Num' instance for 'LaTeXT'.
 -}
 module Text.LaTeX.Base.Monad
  ( LaTeX , (<>)
@@ -31,4 +33,35 @@
 import Text.LaTeX.Base.Types
 import Text.LaTeX.Base.Writer
 import Text.LaTeX.Base.Commands.Monad
+-- Import LaTeX Num instance
+import Text.LaTeX.Base ()
+-- Import 'lift' function
+import Control.Monad.Trans (lift)
 
+-- Num instance for LaTeXT
+
+-- Sadly, we need 'Show' and 'Eq' instances for LaTeXT in order
+-- to do its 'Num' instance.
+
+-- | Don't use it! This instance only exists in order to
+--   define a 'Num' instance to 'LaTeXT'.
+instance Show (LaTeXT m a) where
+ show _   = error "Cannot use \"show\" Show method with a LaTeXT value."
+
+-- | Don't use it! This instance only exists in order to
+--   define a 'Num' instance to 'LaTeXT'.
+instance Eq (LaTeXT m a) where
+ _ == _ = error "Cannot use \"(==)\" Eq method with a LaTeXT value."
+
+-- | Be careful when using 'fromInteger' over a 'LaTeXT' value,
+--   the returned value of the computation is bottom (i.e. 'undefined').
+--   Methods 'abs' and 'signum' are undefined. Don't use them!
+instance Monad m => Num (LaTeXT m a) where
+ (+) = liftOp (+)
+ (-) = liftOp (-)
+ (*) = (>>)
+ negate = liftFun negate
+ fromInteger = fromString . show
+ -- Non-defined methods
+ abs _    = "Cannot use \"abs\" Num method with a LaTeXT value."
+ signum _ = "Cannot use \"signum\" Num method with a LaTeXT value."
diff --git a/Text/LaTeX/Base/Syntax.hs b/Text/LaTeX/Base/Syntax.hs
--- a/Text/LaTeX/Base/Syntax.hs
+++ b/Text/LaTeX/Base/Syntax.hs
@@ -33,7 +33,7 @@
                       -- Use '<>' preferably.
  | TeXEmpty -- ^ An empty expression.
             -- Neutral element of '<>'.
-   deriving Show
+   deriving (Eq,Show)
 
 -- | Alias for 'TeXBraces'.
 braces :: LaTeX -> LaTeX
@@ -46,7 +46,7 @@
  | MOptArg [LaTeX] -- ^ Multiple optional argument.
  | SymArg LaTeX -- ^ An argument enclosed between @\<@ and @\>@.
  | MSymArg [LaTeX] -- ^ Version of 'SymArg' with multiple options.
-   deriving Show
+   deriving (Eq,Show)
 
 -- Monoid instance for 'LaTeX'.
 
@@ -80,5 +80,4 @@
 protectChar '~'  = "\\~{}"
 protectChar '\\' = "\\textbackslash{}"
 protectChar '_'  = "\\_{}"
-protectChar x = [x]
-
+protectChar x = [x]
diff --git a/Text/LaTeX/Base/Types.hs b/Text/LaTeX/Base/Types.hs
--- a/Text/LaTeX/Base/Types.hs
+++ b/Text/LaTeX/Base/Types.hs
@@ -3,7 +3,7 @@
 
 module Text.LaTeX.Base.Types (
    Label
- , createLabel
+ , createLabel , labelName
  , Pos (..)
  , TableSpec (..)
  , Measure (..)
@@ -12,14 +12,20 @@
 import Text.LaTeX.Base.Syntax
 import Text.LaTeX.Base.Render
 
-newtype Label = Label String deriving Show
+newtype Label = Label String deriving (Eq, Show)
 
 createLabel :: String -> Label
-createLabel str = Label str
+createLabel = Label
 
+labelName :: Label -> String
+labelName (Label str) = str
+
 instance Render Label where
  render (Label str) = fromString str
 
+instance IsString Label where
+ fromString = createLabel
+
 data Pos = Bottom | Center | Top deriving Show
 
 instance Render Pos where
@@ -66,3 +72,4 @@
  render (Ex x) = render x <> "ex"
  render (Em x) = render x <> "em"
  render (CustomMeasure x) = render x
+
diff --git a/Text/LaTeX/Base/Warnings.hs b/Text/LaTeX/Base/Warnings.hs
new file mode 100644
--- /dev/null
+++ b/Text/LaTeX/Base/Warnings.hs
@@ -0,0 +1,141 @@
+
+{-# LANGUAGE OverloadedStrings #-}
+
+module Text.LaTeX.Base.Warnings (
+   -- * Warnings datatype
+   Warning (..)
+ , TeXCheck
+ , check
+ , checkFromFunction
+   -- * Several checkings
+ , checkLabels
+ , checkClass
+ , checkDoc
+   -- * Complete checking
+ , checkAll
+ ) where
+
+import Text.LaTeX.Base.Syntax
+import Control.Monad.State
+import Data.Text
+import Data.Maybe
+import Control.Arrow
+import Data.Monoid
+
+-- | List of possible warnings.
+data Warning =
+   UnusedLabel Text    -- ^ There is an unused label. Argument is its name.
+ | UndefinedLabel Text -- ^ There is a reference to an undefined label. Arguments is the name.
+   --
+ | NoClassSelected     -- ^ No class selected with 'documentclass'.
+ | NoDocumentInserted  -- ^ No 'document' inserted.
+   --
+ | CustomWarning Text  -- ^ Custom warning for custom checkings. Use it as you want.
+   deriving (Eq,Show)
+
+-- | A 'TeXCheck' is a function that checks possible warnings from a 'LaTeX' value.
+--   Use the 'Monoid' instance to combine check functions.
+newtype TeXCheck = TC { check :: LaTeX -> [Warning] -- ^ Apply a checking.
+                      }
+-- | Build a 'TeXCheck' from a function.
+checkFromFunction :: (LaTeX -> [Warning]) -> TeXCheck
+checkFromFunction = TC
+
+instance Monoid TeXCheck where
+ mempty = TC $ const []
+ mappend (TC tc1) (TC tc2) = TC $ uncurry mappend . (tc1 &&& tc2)
+
+checkAll :: TeXCheck
+checkAll = mconcat [ checkLabels , checkClass , checkDoc ]
+
+-- Searching for 'documentclass' and 'document'
+
+type BoolSt = State Bool
+
+-- | Check if a document class is specified for the document (using 'documentclass').
+checkClass :: TeXCheck
+checkClass = TC $ \l -> if execState (classcheck l) False then [] else [NoClassSelected]
+
+classcheck :: LaTeX -> BoolSt ()
+classcheck (TeXComm c _) =
+ case c of
+  "documentclass" -> put True
+  _ -> return ()
+classcheck (TeXBraces l) = classcheck l
+classcheck (TeXSeq l1 l2) = classcheck l1 >> classcheck l2
+classcheck _ = return ()
+
+-- | Check if the 'document' environment is called in a 'LaTeX'.
+checkDoc :: TeXCheck
+checkDoc = TC $ \l -> if execState (doccheck l) False then [] else [NoDocumentInserted]
+
+doccheck :: LaTeX -> BoolSt ()
+doccheck (TeXEnv n _ _) =
+ case n of
+  "document" -> put True
+  _ -> return ()
+doccheck (TeXBraces l) = doccheck l
+doccheck (TeXSeq l1 l2) = doccheck l1 >> doccheck l2
+doccheck _ = return ()
+
+-- Checking labels
+
+data LabWarn =
+   RefNoLabel Text
+ | LabelNoRef Text
+ | LabelRef Text
+
+labWarnToWarning :: LabWarn -> Maybe Warning
+labWarnToWarning (RefNoLabel n) = Just $ UndefinedLabel n
+labWarnToWarning (LabelNoRef n) = Just $ UnusedLabel n
+labWarnToWarning _ = Nothing
+
+type LabSt = State [LabWarn]
+
+-- | Checking for unused labels or references tu undefined labels.
+checkLabels :: TeXCheck
+checkLabels = TC $ \l -> catMaybes . fmap labWarnToWarning $ execState (labcheck l) []
+
+labcheck :: LaTeX -> LabSt ()
+labcheck (TeXComm c [FixArg (TeXRaw n)]) =
+ case c of
+  "label"   -> newlab n
+  "ref"     -> newref n
+  "pageref" -> newref n
+labcheck (TeXEnv _ _ l) = labcheck l
+labcheck (TeXMath l) = labcheck l
+labcheck (TeXOp _ l1 l2) = labcheck l1 >> labcheck l2
+labcheck (TeXBraces l) = labcheck l
+labcheck (TeXSeq l1 l2) = labcheck l1 >> labcheck l2
+labcheck _ = return ()
+
+newlab :: Text -> LabSt ()
+newlab n = do
+ st <- get
+ let addLab :: Text -> [LabWarn] -> [LabWarn]
+     addLab n [] = [LabelNoRef n]
+     addLab n l@(x:xs) = let ys = x : addLab n xs in
+       case x of
+        RefNoLabel m -> if n == m then LabelRef n : xs
+                                  else ys
+        LabelNoRef m -> if n == m then l
+                                  else ys
+        LabelRef   m -> if n == m then l
+                                  else ys
+ put $ addLab n st
+
+newref :: Text -> LabSt ()
+newref n = do
+ st <- get
+ let addRef :: Text -> [LabWarn] -> [LabWarn]
+     addRef n [] = [RefNoLabel n]
+     addRef n l@(x:xs) = let ys = x : addRef n xs in
+       case x of
+        RefNoLabel m -> if n == m then l
+                                  else ys
+        LabelNoRef m -> if n == m then LabelRef n : xs
+                                  else ys
+        LabelRef   m -> if n == m then l
+                                  else ys
+ put $ addRef n st
+
diff --git a/Text/LaTeX/Base/Writer.hs b/Text/LaTeX/Base/Writer.hs
--- a/Text/LaTeX/Base/Writer.hs
+++ b/Text/LaTeX/Base/Writer.hs
@@ -6,25 +6,34 @@
    LaTeXT
  , LaTeXT_
  , runLaTeXT
- , execLaTeXT
+ , execLaTeXT
+ , execLaTeXTWarn
  , extractLaTeX
  , extractLaTeX_
- , textell
+ , textell
+ , liftFun
+ , liftOp
    ) where
-
+
 import Control.Monad.Writer
+import Control.Monad.State
 import Control.Applicative
+import Control.Arrow
 import Data.String
 --
 import Text.LaTeX.Base.Syntax
-import Text.LaTeX.Base.Render
+import Text.LaTeX.Base.Render
+import Text.LaTeX.Base.Warnings (Warning,checkAll,check)
+--
+import Control.Monad (liftM)
 
--- | Newtype wrapper over the 'WriterT' monad transformer, with 'LaTeX'
---   as writer state.
 newtype LaTeXT m a =
  LaTeXT { unwrapLaTeXT :: WriterT LaTeX m a }
    deriving (Functor,Applicative,Monad,MonadIO)
 
+instance MonadTrans LaTeXT where
+ lift = LaTeXT . lift
+
 type LaTeXT_ m = LaTeXT m ()
 
 runLaTeXT :: LaTeXT m a -> m (a,LaTeX)
@@ -32,23 +41,60 @@
 
 -- | This is the usual way to run the 'LaTeXT' monad
 --   and obtain a 'LaTeX' value.
-execLaTeXT :: Functor m => LaTeXT m a -> m LaTeX
-execLaTeXT = fmap snd . runLaTeXT
+execLaTeXT :: Monad m => LaTeXT m a -> m LaTeX
+execLaTeXT = liftM snd . runLaTeXT
 
+-- | Version of 'execLaTeXT' with possible warning messages.
+--   This function applies 'checkAll' to the 'LaTeX' output.
+execLaTeXTWarn :: Monad m => LaTeXT m a -> m (LaTeX,[Warning])
+execLaTeXTWarn = liftM (id &&& check checkAll) . execLaTeXT
+
 -- | This function run a 'LaTeXT' computation,
 --   lifting the result again in the monad.
 extractLaTeX :: Monad m => LaTeXT m a -> LaTeXT m (a,LaTeX)
 extractLaTeX = LaTeXT . lift . runLaTeXT
 
 extractLaTeX_ :: Monad m => LaTeXT m a -> LaTeXT m LaTeX
-extractLaTeX_ = (>>= return . snd) . LaTeXT . lift . runLaTeXT
+extractLaTeX_ = liftM snd . extractLaTeX
 
 -- | With 'textell' you can append 'LaTeX' values to the
 --   state of the 'LaTeXT' monad.
 textell :: Monad m => LaTeX -> LaTeXT m ()
 textell = LaTeXT . tell
 
+-- | Lift a function over 'LaTeX' values to a function
+--   acting over the state of a 'LaTeXT' computation.
+liftFun :: Monad m
+        => (LaTeX -> LaTeX)
+        -> (LaTeXT m a -> LaTeXT m a)
+liftFun f ml = do
+ (a,l') <- lift $ do
+            (a,l) <- runLaTeXT ml
+            let l' = f l
+            return (a,l')
+ textell l'
+ return a
+
+-- | Lift an operator over 'LaTeX' values to an operator
+--   acting over the state of two 'LaTeXT' computations.
+--
+-- /Note: The returned value is the one returned by the/
+-- /second argument of the lifted operator./
+liftOp :: Monad m
+       => (LaTeX -> LaTeX -> LaTeX)
+       -> (LaTeXT m a -> LaTeXT m a -> LaTeXT m a)
+liftOp op ml1 ml2 = do
+ (a,l') <- lift $ do
+            (_,l1) <- runLaTeXT ml1
+            (a,l2) <- runLaTeXT ml2
+            let l' = l1 `op` l2
+            return (a,l')
+ textell l'
+ return a
+
 -- Overloaded Strings
 
+-- | Be careful when using 'fromString' over a 'LaTeXT' value,
+--   the returned value of the computation is bottom (i.e. 'undefined').
 instance Monad m => IsString (LaTeXT m a) where
- fromString = (>> return undefined) . textell . fromString
+ fromString = (>> return undefined) . textell . fromString
diff --git a/Text/LaTeX/Packages.hs b/Text/LaTeX/Packages.hs
--- a/Text/LaTeX/Packages.hs
+++ b/Text/LaTeX/Packages.hs
@@ -9,6 +9,7 @@
    -- * Mathematics packages
  , module Text.LaTeX.Packages.AMSMath
  , module Text.LaTeX.Packages.AMSFonts
+ , module Text.LaTeX.Packages.AMSThm
    -- * Graphics packages
  , module Text.LaTeX.Packages.Color
    ) where
@@ -18,4 +19,5 @@
 import Text.LaTeX.Packages.Beamer
 import Text.LaTeX.Packages.AMSMath
 import Text.LaTeX.Packages.AMSFonts
+import Text.LaTeX.Packages.AMSThm
 import Text.LaTeX.Packages.Color
diff --git a/Text/LaTeX/Packages/AMSFonts.hs b/Text/LaTeX/Packages/AMSFonts.hs
--- a/Text/LaTeX/Packages/AMSFonts.hs
+++ b/Text/LaTeX/Packages/AMSFonts.hs
@@ -1,4 +1,6 @@
 
+{-# OPTIONS_HATEX MakeMonadic #-}
+
 module Text.LaTeX.Packages.AMSFonts
  ( -- * AMSFonts package
    amsfonts
diff --git a/Text/LaTeX/Packages/AMSMath.hs b/Text/LaTeX/Packages/AMSMath.hs
--- a/Text/LaTeX/Packages/AMSMath.hs
+++ b/Text/LaTeX/Packages/AMSMath.hs
@@ -1,4 +1,5 @@
 {-# LANGUAGE OverloadedStrings #-}
+{-# OPTIONS_HATEX MakeMonadic #-}
 
 module Text.LaTeX.Packages.AMSMath
  ( -- * AMSMath package
@@ -9,13 +10,22 @@
    -- ** Superscript and subscript
  , (^:) , (!:)
    -- ** Function symbols
+   -- | Some symbols are preceded with /t/ to be distinguished from
+   --   predefined Haskell entities (like 'sin' and 'cos').
  , tsin , arcsin
  , tcos , arccos
  , ttan , arctan
  , texp
  , tlog , ln
+   -- ** Operator symbols
+ , (=:) , (/=:)
+ , (>:) , (>=:)
+ , (<:) , (<=:)
+ , in_ , ni , notin
    -- ** Other symbols
  , to
+ , forall
+ , dagger, ddagger
    -- * Fonts
  , mathbf
  , mathrm
@@ -26,7 +36,7 @@
    ) where
 
 import Text.LaTeX.Base.Syntax
-import Text.LaTeX.Base.Commands (raw)
+import Text.LaTeX.Base.Commands (raw,between)
 
 -- | AMSMath package.
 -- Example:
@@ -87,11 +97,62 @@
 ln :: LaTeX
 ln = TeXComm "ln" []
 
+---- Operator symbols
+
+-- | Negative form of an operator.
+notop :: (LaTeX -> LaTeX -> LaTeX)
+      -> (LaTeX -> LaTeX -> LaTeX)
+notop op =
+ \l1 l2 ->
+   (l1 <> TeXCommS "not") `op` l2
+
+infix 4 =: , /=:
+
+(=:),(/=:) :: LaTeX -> LaTeX -> LaTeX
+(=:)  = TeXOp "="
+(/=:) = notop (=:)
+
+-- | Greater.
+(>:) :: LaTeX -> LaTeX -> LaTeX
+(>:) = TeXOp ">"
+
+-- | Greater or equal.
+(>=:) :: LaTeX -> LaTeX -> LaTeX
+(>=:) = between $ TeXComm "geq" []
+
+-- | Lesser.
+(<:) :: LaTeX -> LaTeX -> LaTeX
+(<:) = TeXOp "<"
+
+-- | Lesser or equal.
+(<=:) :: LaTeX -> LaTeX -> LaTeX
+(<=:) = between $ TeXComm "leq" []
+
+in_ :: LaTeX -> LaTeX -> LaTeX
+in_ = between $ TeXComm "in" []
+
+ni :: LaTeX -> LaTeX -> LaTeX
+ni  = between $ TeXComm "ni" []
+
+notin :: LaTeX -> LaTeX -> LaTeX
+notin = between $ TeXComm "notin" []
+
 ---- Other symbols
 
 -- | A right-arrow.
 to :: LaTeX
 to = TeXComm "to" []
+
+forall :: LaTeX
+forall = TeXComm "forall" []
+
+-- | Dagger symbol.
+dagger :: LaTeX
+dagger = TeXComm "dagger" []
+
+-- | Double dagger symbol.
+ddagger :: LaTeX
+ddagger = TeXComm "ddagger" []
 
 -------------------------------------
 ------------ Math Fonts -------------
diff --git a/Text/LaTeX/Packages/AMSMath/Monad.hs b/Text/LaTeX/Packages/AMSMath/Monad.hs
--- a/Text/LaTeX/Packages/AMSMath/Monad.hs
+++ b/Text/LaTeX/Packages/AMSMath/Monad.hs
@@ -17,13 +17,22 @@
    -- ** Superscript and subscript
  , (^:) , (!:)
    -- ** Function symbols
+   -- | Some symbols are preceded with /t/ to be distinguished from
+   --   predefined Haskell entities (like 'sin' and 'cos').
  , tsin , arcsin
  , tcos , arccos
  , ttan , arctan
  , texp
  , tlog , ln
+   -- ** Operator symbols
+ , (=:) , (/=:)
+ , (>:) , (>=:)
+ , (<:) , (<=:)
+ , in_ , ni , notin
    -- ** Other symbols
  , to
+ , forall
+ , dagger, ddagger
    -- * Fonts
  , mathbf
  , mathrm
@@ -114,10 +123,87 @@
 ln ::   (Monad m) => LaTeXT_ m
 ln = do textell ( App.ln)
 
+
+(=:) ::   (Monad m) => LaTeXT_ m -> LaTeXT_ m -> LaTeXT_ m
+(=:) a1 a2
+  = do a1 <- extractLaTeX_ a1
+       a2 <- extractLaTeX_ a2
+       textell ( (App.=:) a1 a2)
+
+
+(/=:) ::   (Monad m) => LaTeXT_ m -> LaTeXT_ m -> LaTeXT_ m
+(/=:) a1 a2
+  = do a1 <- extractLaTeX_ a1
+       a2 <- extractLaTeX_ a2
+       textell ( (App./=:) a1 a2)
+
+
+(>:) ::   (Monad m) => LaTeXT_ m -> LaTeXT_ m -> LaTeXT_ m
+(>:) a1 a2
+  = do a1 <- extractLaTeX_ a1
+       a2 <- extractLaTeX_ a2
+       textell ( (App.>:) a1 a2)
+
+
+(>=:) ::   (Monad m) => LaTeXT_ m -> LaTeXT_ m -> LaTeXT_ m
+(>=:) a1 a2
+  = do a1 <- extractLaTeX_ a1
+       a2 <- extractLaTeX_ a2
+       textell ( (App.>=:) a1 a2)
+
+
+(<:) ::   (Monad m) => LaTeXT_ m -> LaTeXT_ m -> LaTeXT_ m
+(<:) a1 a2
+  = do a1 <- extractLaTeX_ a1
+       a2 <- extractLaTeX_ a2
+       textell ( (App.<:) a1 a2)
+
+
+(<=:) ::   (Monad m) => LaTeXT_ m -> LaTeXT_ m -> LaTeXT_ m
+(<=:) a1 a2
+  = do a1 <- extractLaTeX_ a1
+       a2 <- extractLaTeX_ a2
+       textell ( (App.<=:) a1 a2)
+
+
+in_ ::   (Monad m) => LaTeXT_ m -> LaTeXT_ m -> LaTeXT_ m
+in_ a1 a2
+  = do a1 <- extractLaTeX_ a1
+       a2 <- extractLaTeX_ a2
+       textell ( App.in_ a1 a2)
+
+
+ni ::   (Monad m) => LaTeXT_ m -> LaTeXT_ m -> LaTeXT_ m
+ni a1 a2
+  = do a1 <- extractLaTeX_ a1
+       a2 <- extractLaTeX_ a2
+       textell ( App.ni a1 a2)
+
+
+notin ::   (Monad m) => LaTeXT_ m -> LaTeXT_ m -> LaTeXT_ m
+notin a1 a2
+  = do a1 <- extractLaTeX_ a1
+       a2 <- extractLaTeX_ a2
+       textell ( App.notin a1 a2)
+
 -- | A right-arrow.
 
 to ::   (Monad m) => LaTeXT_ m
 to = do textell ( App.to)
+
+
+forall ::   (Monad m) => LaTeXT_ m
+forall = do textell ( App.forall)
+
+-- | Dagger symbol.
+
+dagger ::   (Monad m) => LaTeXT_ m
+dagger = do textell ( App.dagger)
+
+-- | Double dagger symbol.
+
+ddagger ::   (Monad m) => LaTeXT_ m
+ddagger = do textell ( App.ddagger)
 
 
 mathbf ::   (Monad m) => LaTeXT_ m -> LaTeXT_ m
diff --git a/Text/LaTeX/Packages/AMSThm.hs b/Text/LaTeX/Packages/AMSThm.hs
new file mode 100644
--- /dev/null
+++ b/Text/LaTeX/Packages/AMSThm.hs
@@ -0,0 +1,69 @@
+
+{-# OPTIONS_HATEX MakeMonadic #-}
+{-# LANGUAGE OverloadedStrings #-}
+
+-- | Package for theorem environments.
+module Text.LaTeX.Packages.AMSThm
+ ( -- * AMSThm package
+   amsthm
+   -- * AMSThm functions
+ , newtheorem
+ , theorem
+ , proof
+ , qedhere
+ , TheoremStyle (..)
+ , theoremstyle
+   ) where
+
+import Text.LaTeX.Base.Syntax
+import Text.LaTeX.Base.Render
+
+-- | AMSThm package.
+-- Example:
+--
+-- > usepackage [] amsthm
+amsthm :: String
+amsthm = "amsthm"
+
+-- | Create a new 'theorem' environment type.
+--   Arguments are environment name (this will be the argument
+--   when using the 'theorem' function) and the displayed title.
+--
+--   For example:
+--
+-- > newtheorem "prop" "Proposition"
+--
+-- > theorem "prop" "This is it."
+newtheorem :: String -> LaTeX -> LaTeX
+newtheorem str l = TeXComm "newtheorem" [ FixArg $ fromString str , FixArg l ]
+
+theorem :: String -> LaTeX -> LaTeX
+theorem str l = TeXEnv str [] l
+
+-- | The 'proof' environment. The first optional argument
+--   is used to put a custom title to the proof.
+proof :: Maybe LaTeX -> LaTeX -> LaTeX
+proof  Nothing l = TeXEnv "proof" [ ] l
+proof (Just n) l = TeXEnv "proof" [ OptArg n ] l
+
+-- | Insert the /QED/ symbol.
+qedhere :: LaTeX
+qedhere = TeXComm "qedhere" []
+
+data TheoremStyle =
+   Plain
+ | Definition
+ | Remark
+ | CustomThmStyle String
+   deriving Show
+
+instance Render TheoremStyle where
+ render Plain = "plain"
+ render Definition = "definition"
+ render Remark = "remark"
+ render (CustomThmStyle str) = fromString str
+
+-- | Set the theorem style. Call this function in the preamble.
+theoremstyle :: TheoremStyle -> LaTeX
+theoremstyle thmsty = TeXComm "theoremstyle" [ FixArg $ TeXRaw $ render thmsty ]
+
diff --git a/Text/LaTeX/Packages/AMSThm/Monad.hs b/Text/LaTeX/Packages/AMSThm/Monad.hs
new file mode 100644
--- /dev/null
+++ b/Text/LaTeX/Packages/AMSThm/Monad.hs
@@ -0,0 +1,84 @@
+{-# LANGUAGE OverloadedStrings #-}
+
+-- | Package for theorem environments.
+-- 
+-- /For contributors: This module was automatically generated by HaTeX-meta./
+-- /So, please, don't make any change here directly, because/
+-- /this is intended to be generated from/
+-- "Text.LaTeX.Packages.AMSThm" /module via HaTeX-meta,/
+-- /and therefore, changes must to be done in these places./
+
+module Text.LaTeX.Packages.AMSThm.Monad
+ ( -- * AMSThm package
+   amsthm
+   -- * AMSThm functions
+ , newtheorem
+ , theorem
+ , proof
+ , qedhere
+ , TheoremStyle (..)
+ , theoremstyle
+   ) where
+
+import Text.LaTeX.Base.Writer
+import Text.LaTeX.Base.Render
+import Text.LaTeX.Base.Types
+import qualified Text.LaTeX.Packages.AMSThm as App
+import Text.LaTeX.Packages.AMSThm(TheoremStyle)
+
+{-|
+AMSThm package.
+ Example:
+
+>  usepackage [] amsthm
+
+-}
+amsthm :: String
+amsthm = App.amsthm
+
+{-|
+Create a new 'theorem' environment type.
+   Arguments are environment name (this will be the argument
+   when using the 'theorem' function) and the displayed title.
+For example:
+
+>  newtheorem "prop" "Proposition"
+
+
+>  theorem "prop" "This is it."
+
+-}
+newtheorem ::   (Monad m) => String -> LaTeXT_ m -> LaTeXT_ m
+newtheorem a1 a2
+  = do a2 <- extractLaTeX_ a2
+       textell ( App.newtheorem a1 a2)
+
+
+theorem ::   (Monad m) => String -> LaTeXT_ m -> LaTeXT_ m
+theorem a1 a2
+  = do a2 <- extractLaTeX_ a2
+       textell ( App.theorem a1 a2)
+
+{-|
+The 'proof' environment. The first optional argument
+   is used to put a custom title to the proof.
+-}
+proof ::   (Monad m) => Maybe (LaTeXT_ m) -> LaTeXT_ m -> LaTeXT_ m
+proof a1 a2
+  = do a1 <- maybe (return Nothing)
+               ((>>= return . Just) . extractLaTeX_)
+               a1
+       a2 <- extractLaTeX_ a2
+       textell ( App.proof a1 a2)
+
+-- | Insert the /QED/ symbol.
+
+qedhere ::   (Monad m) => LaTeXT_ m
+qedhere = do textell ( App.qedhere)
+
+-- | Set the theorem style. Call this function in the preamble.
+
+theoremstyle ::   (Monad m) => TheoremStyle -> LaTeXT_ m
+theoremstyle a1 = do textell ( App.theoremstyle a1)
+
+
diff --git a/Text/LaTeX/Packages/Beamer.hs b/Text/LaTeX/Packages/Beamer.hs
--- a/Text/LaTeX/Packages/Beamer.hs
+++ b/Text/LaTeX/Packages/Beamer.hs
@@ -1,4 +1,5 @@
-{-# LANGUAGE OverloadedStrings #-}
+{-# LANGUAGE OverloadedStrings #-}
+{-# OPTIONS_HATEX MakeMonadic #-}
 
 module Text.LaTeX.Packages.Beamer
  ( -- * Beamer package
@@ -27,7 +28,7 @@
 -- | The 'beamer' document class. Importing a package is not required. Example:
 --
 -- > documentclass [] beamer
-beamer :: LaTeX
+beamer :: String
 beamer = "beamer"
 
 -- | A presentation is composed of a sequence of frames. Each frame is created with this function.
diff --git a/Text/LaTeX/Packages/Beamer/Monad.hs b/Text/LaTeX/Packages/Beamer/Monad.hs
--- a/Text/LaTeX/Packages/Beamer/Monad.hs
+++ b/Text/LaTeX/Packages/Beamer/Monad.hs
@@ -40,8 +40,8 @@
 >  documentclass [] beamer
 
 -}
-beamer ::   (Monad m) => LaTeXT_ m
-beamer = do textell ( App.beamer)
+beamer :: String
+beamer = App.beamer
 
 -- | A presentation is composed of a sequence of frames. Each frame is created with this function.
 
diff --git a/Text/LaTeX/Packages/Color.hs b/Text/LaTeX/Packages/Color.hs
--- a/Text/LaTeX/Packages/Color.hs
+++ b/Text/LaTeX/Packages/Color.hs
@@ -1,5 +1,6 @@
 
 {-# LANGUAGE OverloadedStrings #-}
+{-# OPTIONS_HATEX MakeMonadic #-}
 
 module Text.LaTeX.Packages.Color
  ( -- * Color package
diff --git a/Text/LaTeX/Packages/Hyperref.hs b/Text/LaTeX/Packages/Hyperref.hs
--- a/Text/LaTeX/Packages/Hyperref.hs
+++ b/Text/LaTeX/Packages/Hyperref.hs
@@ -1,5 +1,6 @@
 
 {-# LANGUAGE OverloadedStrings #-}
+{-# OPTIONS_HATEX MakeMonadic #-}
 
 module Text.LaTeX.Packages.Hyperref
  ( -- * Hyperref package
diff --git a/Text/LaTeX/Packages/Inputenc.hs b/Text/LaTeX/Packages/Inputenc.hs
--- a/Text/LaTeX/Packages/Inputenc.hs
+++ b/Text/LaTeX/Packages/Inputenc.hs
@@ -1,5 +1,6 @@
 
 {-# LANGUAGE OverloadedStrings #-}
+{-# OPTIONS_HATEX MakeMonadic #-}
 
 module Text.LaTeX.Packages.Inputenc
  ( -- * Inputenc package
diff --git a/Text/LaTeX/Packages/Monad.hs b/Text/LaTeX/Packages/Monad.hs
--- a/Text/LaTeX/Packages/Monad.hs
+++ b/Text/LaTeX/Packages/Monad.hs
@@ -9,6 +9,7 @@
    -- * Mathematics packages
  , module Text.LaTeX.Packages.AMSMath.Monad
  , module Text.LaTeX.Packages.AMSFonts.Monad
+ , module Text.LaTeX.Packages.AMSThm.Monad
    -- * Graphics packages
  , module Text.LaTeX.Packages.Color.Monad
    ) where
@@ -18,4 +19,5 @@
 import Text.LaTeX.Packages.Beamer.Monad
 import Text.LaTeX.Packages.AMSMath.Monad
 import Text.LaTeX.Packages.AMSFonts.Monad
+import Text.LaTeX.Packages.AMSThm.Monad
 import Text.LaTeX.Packages.Color.Monad