diff --git a/GTALib.cabal b/GTALib.cabal
--- a/GTALib.cabal
+++ b/GTALib.cabal
@@ -7,7 +7,7 @@
 -- The package version. See the Haskell package versioning policy
 -- (http://www.haskell.org/haskellwiki/Package_versioning_policy) for
 -- standards guiding when and how versions should be incremented.
-Version:             0.0.1
+Version:             0.0.2
 
 -- A short (one-line) description of the package.
 Synopsis: A library for GTA programming           
@@ -57,7 +57,7 @@
   -- Packages needed in order to build this package.
   Build-depends:    base>=4.3 && < 4.6,template-haskell>=2.5 && <2.8,containers>=0.4 && <0.6,parallel >=3.1 && < 3.3
   HS-source-dirs:   src/
-  --GHC-options:    -Wall   -O
+  -- GHC-options:    -Wall   -O
   
   -- Modules not exported by this package.
   -- Other-modules:       
diff --git a/src/GTA/Data/JoinList.hs b/src/GTA/Data/JoinList.hs
--- a/src/GTA/Data/JoinList.hs
+++ b/src/GTA/Data/JoinList.hs
@@ -1,7 +1,8 @@
 {-# LANGUAGE MultiParamTypeClasses,FlexibleInstances,FlexibleContexts,FunctionalDependencies,UndecidableInstances,RankNTypes,ExplicitForAll,ScopedTypeVariables,NoMonomorphismRestriction,OverlappingInstances,EmptyDataDecls,RecordWildCards,TypeFamilies,TemplateHaskell  #-}
 
-module GTA.Data.JoinList (JoinList(Times, Single, Nil), JoinListAlgebra(JoinListAlgebra), times, single, nil, joinize, dejoinize, segs, inits, tails, subs, assigns, paths, mapJ, count, maxsum, maxsumsolution, maxsumWith, maxsumKWith, maxsumsolutionXKWith, maxsumsolutionXWith, maxsumsolutionWith, maxsumsolutionKWith, maxprodWith, maxprodKWith, maxprodsolutionXKWith, maxprodsolutionXWith, maxprodsolutionWith, maxprodsolutionKWith, segsP, initsP, tailsP, subsP, assignsP) where
+module GTA.Data.JoinList (JoinList(Times, Single, Nil), JoinListAlgebra(JoinListAlgebra), times, single, nil, joinize, dejoinize, segs, inits, tails, subs, assigns, paths, mapJ, count, maxsum, maxsumsolution, maxsumWith, maxsumKWith, maxsumsolutionXKWith, maxsumsolutionXWith, maxsumsolutionWith, maxsumsolutionKWith, maxprodWith, maxprodKWith, maxprodsolutionXKWith, maxprodsolutionXWith, maxprodsolutionWith, maxprodsolutionKWith, segsP, initsP, tailsP, subsP, assignsP, crossConcat, bagOfSingleton, emptyBag, bagOfNil, bagUnion, Semiring) where
 
+
 import GTA.Core
 import GTA.Util.GenericSemiringStructureTemplate
 import GTA.Data.BinTree (BinTree (..))
@@ -15,6 +16,7 @@
                 | Nil
 --             deriving (Show, Eq, Ord, Read)
 
+-- stupid joinize function
 joinize :: forall a. [a] -> JoinList a
 joinize [] = Nil
 joinize [a] = Single a
@@ -23,6 +25,7 @@
                 d = (n `div` 2)
             in Times (joinize x1) (joinize x2)
 
+-- stupid dejoinize function
 dejoinize :: forall a. JoinList a -> [a]
 dejoinize (Times x1 x2) = dejoinize x1 ++ dejoinize x2
 dejoinize (Single a) = [a]
@@ -201,3 +204,23 @@
                     p2 = h (n-1) x2
           h _ (Single a) = single a
           h _ Nil = nil
+
+--- useful functions to design generators: constructors of bags of lists
+crossConcat :: Bag (JoinList a) -> Bag (JoinList a) -> Bag (JoinList a)
+crossConcat = times (algebra freeSemiring)
+
+bagOfSingleton :: a -> Bag (JoinList a)
+bagOfSingleton = single (algebra freeSemiring)
+
+bagOfNil :: Bag (JoinList a)
+bagOfNil =  nil (algebra freeSemiring)
+
+emptyBag :: Bag (JoinList a)
+emptyBag = let GenericSemiring{..} = freeSemiring :: GenericSemiring (JoinListAlgebra a) (Bag (JoinList a))
+           in identity monoid 
+
+bagUnion :: Bag (JoinList a) -> Bag (JoinList a) -> Bag (JoinList a)
+bagUnion = let GenericSemiring{..} = freeSemiring :: GenericSemiring (JoinListAlgebra a) (Bag (JoinList a))
+           in oplus monoid
+
+