diff --git a/requirements.txt b/requirements.txt
index 26cfeb5..90d7a0d 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -1,3 +1,4 @@
 click
 pytest
+pytest-ordering
 http://www.opengrm.org/twiki/pub/GRM/PyniniDownload/pynini-2.0.0.tar.gz#egg=pynini
diff --git a/tests/test_fsts.py b/tests/test_fsts.py
new file mode 100644
index 0000000..916fe10
--- /dev/null
+++ b/tests/test_fsts.py
@@ -0,0 +1,20 @@
+# -*- coding: utf-8 -*-
+
+import sys
+import os
+import pytest
+import pynini
+
+sys.path.insert(0, os.path.abspath(os.path.join(os.path.dirname(__file__), '../timur')))
+
+from timur import fsts
+from timur import helpers
+
+sample_symbols = ["<Base_Stems>", "<NN>", "<base>", "<frei>", "<NMasc_es_e>"]
+
+def test_map_fst():
+    syms = helpers.load_alphabet(sample_symbols)
+    assert(True)
+
+if __name__ == '__main__':
+    unittest.main()
diff --git a/tests/test_helpers.py b/tests/test_helpers.py
index 455fd4e..9e08d84 100644
--- a/tests/test_helpers.py
+++ b/tests/test_helpers.py
@@ -1,7 +1,8 @@
 # -*- coding: utf-8 -*-
 
-import sys, os, pytest
-
+import sys
+import os
+import pytest
 import pynini
 
 sys.path.insert(0, os.path.abspath(os.path.join(os.path.dirname(__file__), '../timur')))
@@ -11,6 +12,7 @@
 sample_symbols = ["<Base_Stems>", "<NN>", "<base>", "<frei>", "<NMasc_es_e>"]
 sample_entries = ["<Base_Stems>Anüs<NN><base><frei><NMasc_es_e>"]
 
+@pytest.mark.first
 def test_load_alphabet():
     '''
     Load the sample symbol set and check for membership.
@@ -19,6 +21,7 @@ def test_load_alphabet():
     assert(syms.member("<NN>"))
     assert(syms.member("ü"))
 
+@pytest.mark.second
 def test_load_lexicon():
     '''
     Load the sample lexicon and check vor invariance.
diff --git a/timur/data/syms.txt b/timur/data/syms.txt
index 39ab4f5..f52a59c 100644
--- a/timur/data/syms.txt
+++ b/timur/data/syms.txt
@@ -18,12 +18,35 @@
 <V>
 <ORD>
 <OTHER>
+<PREF>
+<KSF>
+<CARD,DIGCARD,NE>
+<ADJ,CARD>
+<ADJ,NN>
+<CARD,NN>
+<CARD,NE>
+<ABK,ADJ,NE,NN>
+<ADJ,NE,NN>
+<ABK,NE,NN>
+<NE,NN>
+<ABK,CARD,NN>
+<ABK,NN>
+<ADJ,CARD,NN,V>
+<ADJ,NN,V>
+<ABK,ADJ,NE,NN,V>
+<ADJ,NE,NN,V>
+<ADV,NE,NN,V>
+<ABK,NE,NN,V>
+<NE,NN,V>
+<ABK,NN,V>
+<NN,V>
 # intermediate features
 <QUANT>
 <Initial>
 <Base_Stems>
 <Deriv_Stems>
 <Kompos_Stems>
+<Pref_Stems>
 # stem type features
 <base>
 <deriv>
diff --git a/timur/fsts/__init__.py b/timur/fsts/__init__.py
index 35eab7c..1563752 100644
--- a/timur/fsts/__init__.py
+++ b/timur/fsts/__init__.py
@@ -1,2 +1,4 @@
 from .num_fst import num_fst
 from .phon_fst import phon_fst
+from .map_fst import map_fst_map1
+from .map_fst import map_fst_map2
diff --git a/timur/fsts/map_fst.py b/timur/fsts/map_fst.py
new file mode 100644
index 0000000..6df5aac
--- /dev/null
+++ b/timur/fsts/map_fst.py
@@ -0,0 +1,24 @@
+# -*- coding: utf-8 -*- 
+from __future__ import absolute_import
+
+import pynini
+
+from timur.helpers import union
+from timur.helpers import concat
+
+def map_fst_map1(symbol_table):
+    '''
+    Modifications of lexical entries
+    '''
+    
+    # lexical features to be omitted from the output
+    cat = pynini.string_map(["<ABK>", "<ADJ>", "<ADV>", "<CARD>", "<DIGCARD>", "<NE>", "<NN>", "<PRO>", "<V>", "<ORD>", "<OTHER>", "<KSF>"], input_token_type=symbol_table, output_token_type=symbol_table)
+
+    cat_ext = pynini.string_map(["<ABK>", "<ADJ>", "<ADV>", "<CARD>", "<DIGCARD>", "<NE>", "<NN>", "<PRO>", "<V>", "<ORD>", "<OTHER>", "<CARD,DIGCARD,NE>", "<ADJ,CARD>", "<ADJ,NN>", "<CARD,NN>", "<CARD,NE>", "<ABK,ADJ,NE,NN>", "<ADJ,NE,NN>", "<ABK,NE,NN>", "<NE,NN>", "<ABK,CARD,NN>", "<ABK,NN>", "<ADJ,CARD,NN,V>", "<ADJ,NN,V>", "<ABK,ADJ,NE,NN,V>", "<ADJ,NE,NN,V>", "<ADV,NE,NN,V>", "<ABK,NE,NN,V>", "<NE,NN,V>", "<ABK,NN,V>", "<NN,V>"], input_token_type=symbol_table, output_token_type=symbol_table)
+
+    return pynini.Fst()
+
+def map_fst_map2(symbol_table):
+    '''
+    Modifications of lexical entries
+    '''
diff --git a/timur/helpers/helpers.py b/timur/helpers/helpers.py
index 4ac36aa..1336fa2 100644
--- a/timur/helpers/helpers.py
+++ b/timur/helpers/helpers.py
@@ -4,7 +4,7 @@
 def union(*args, token_type="utf8"):
     args_mod = []
     for arg in args:
-        if type(args) == "str":
+        if isinstance(arg, str):
             args_mod.append(pynini.acceptor(arg, token_type=token_type))
         else:
             args_mod.append(arg)
@@ -13,8 +13,13 @@ def union(*args, token_type="utf8"):
 def concat(*args, token_type="utf8"):
     args_mod = []
     conc = pynini.Fst()
+    conc.set_start(conc.add_state())
+    conc.set_final(conc.start())
+    if isinstance(token_type, pynini.SymbolTable):
+        conc.set_input_symbols(token_type)
+        conc.set_output_symbols(token_type)
     for arg in args:
-        if type(args) == "str":
+        if isinstance(arg, str):
             arg = pynini.acceptor(arg, token_type=token_type)
         conc = pynini.concat(conc, arg)
     return conc
@@ -30,7 +35,8 @@ def load_alphabet(source, auto_singletons=True):
             if symbol.isprintable() and not symbol.isspace():
                 syms.add_symbol(symbol)
     for symbol in source:
-        symbol = str(symbol)
+        if isinstance(symbol, bytes):
+            symbol = symbol.decode("utf-8")
         if symbol.startswith('#'):
             continue
         syms.add_symbol(symbol.strip())
diff --git a/timur/scripts/timur.py b/timur/scripts/timur.py
index b0513cb..2336f11 100644
--- a/timur/scripts/timur.py
+++ b/timur/scripts/timur.py
@@ -36,8 +36,25 @@ def build(lexicon):
 
     lex = helpers.load_lexicon(lexicon, syms)
 
-    #phon = phon_fst(syms)
-    #phon.draw("test.dot")
-    num_stems = fsts.num_fst(syms)
+    # add repetitive prefixes
+    # TODO: move to fst function
+    print(syms.member("<Pref_Stems>"))
+    repeatable_prefs = helpers.concat(
+        "<Pref_Stems>",
+        helpers.union(
+            "u r <PREF>",
+            "v o r <PREF>",
+            token_type=syms
+            ).closure(1),
+        "<ADJ,NN> <nativ>",
+        token_type=syms
+        )
+    lex = pynini.union(lex, repeatable_prefs)
+
+    map1 = fsts.map_fst_map1(syms)
+
+    lex = pynini.compose(map1, lex)
+    lex.draw("test.dot")
 
-    ANY = construct_any(syms)
+    #phon = phon_fst(syms)
+    #num_stems = fsts.num_fst(syms)