diff --git a/README.rst b/README.rst
index 7b12126..207238b 100644
--- a/README.rst
+++ b/README.rst
@@ -14,6 +14,22 @@ Requires
 Changes
 =======
 
+*6.0.4 - 05.06.2023*
+
+- code optimized
+
+*6.0.3 - 05.02.2023*
+
+- updt: remove left/right fields
+
+*6.0.2 - 08.11.2022*
+
+- add: show linked cashbook on category-form
+
+*6.0.1 - 08.11.2022*
+
+- works
+
 *6.0.0 - 07.11.2022*
 
 - init
diff --git a/__init__.py b/__init__.py
index 11bfdee..e8af3da 100644
--- a/__init__.py
+++ b/__init__.py
@@ -7,6 +7,7 @@ from trytond.pool import Pool
 from .category import Category
 from .book import CategoryCashbookRel, Cashbook
 
+
 def register():
     Pool.register(
         Category,
diff --git a/book.py b/book.py
index 65f0839..00a2d5e 100644
--- a/book.py
+++ b/book.py
@@ -3,14 +3,14 @@
 # this repository contains the full copyright notices and license terms.
 
 from trytond.model import ModelSQL, fields
-from trytond.transaction import Transaction
-from trytond.pool import Pool, PoolMeta
+from trytond.pool import PoolMeta
 
 
 class Cashbook(metaclass=PoolMeta):
     __name__ = 'cashbook.book'
 
-    categories = fields.Many2Many(string='Categories',
+    categories = fields.Many2Many(
+        string='Categories',
         relation_name='cashbook.bookcategory-rel',
         origin='cashbook', target='category')
 
@@ -21,9 +21,11 @@ class CategoryCashbookRel(ModelSQL):
     'Category Cashbook Relation'
     __name__ = 'cashbook.bookcategory-rel'
 
-    category = fields.Many2One(string='Category', required=True, select=True,
+    category = fields.Many2One(
+        string='Category', required=True, select=True,
         model_name='cashbook.bookcategory', ondelete='CASCADE')
-    cashbook = fields.Many2One(string='Cashbook', required=True, select=True,
+    cashbook = fields.Many2One(
+        string='Cashbook', required=True, select=True,
         model_name='cashbook.book', ondelete='CASCADE')
 
 # end CategoryCashbookRel
diff --git a/category.py b/category.py
index 06160cc..b428e51 100644
--- a/category.py
+++ b/category.py
@@ -11,31 +11,35 @@ class Category(tree(separator=' / '), ModelSQL, ModelView):
     "Cashbook Category"
     __name__ = "cashbook.bookcategory"
 
-    company = fields.Many2One(string='Company', model_name='company.company',
+    company = fields.Many2One(
+        string='Company', model_name='company.company',
         required=True, ondelete="RESTRICT")
     name = fields.Char(string='Name', required=True, translate=True)
 
-    parent = fields.Many2One(string='Parent', select=True,
-        model_name='cashbook.bookcategory', ondelete='CASCADE',
-        left='left', right='right')
-    childs = fields.One2Many(string='Children', field='parent',
+    parent = fields.Many2One(
+        string='Parent', select=True,
+        model_name='cashbook.bookcategory', ondelete='CASCADE')
+    childs = fields.One2Many(
+        string='Children', field='parent',
         model_name='cashbook.bookcategory')
-    left = fields.Integer(string='Left', required=True, select=True)
-    right = fields.Integer(string='Right', required=True, select=True)
+
+    cashbooks = fields.Many2Many(
+        string='Cashbooks',
+        relation_name='cashbook.bookcategory-rel',
+        origin='category', target='cashbook')
+
+    @classmethod
+    def __register__(cls, module_name):
+        super(Category, cls).__register__(module_name)
+        table = cls.__table_handler__(module_name)
+        table.drop_column('left')
+        table.drop_column('right')
 
     @classmethod
     def __setup__(cls):
         super(Category, cls).__setup__()
         cls._order.insert(0, ('rec_name', 'ASC'))
 
-    @staticmethod
-    def default_left():
-        return 0
-
-    @staticmethod
-    def default_right():
-        return 0
-
     @staticmethod
     def default_company():
         return Transaction().context.get('company') or None
diff --git a/locale/de.po b/locale/de.po
index 2372d4e..94fce9d 100644
--- a/locale/de.po
+++ b/locale/de.po
@@ -54,6 +54,10 @@ msgctxt "view:cashbook.bookcategory:"
 msgid "General Information"
 msgstr "Allgemein"
 
+msgctxt "view:cashbook.bookcategory:"
+msgid "Cashbooks"
+msgstr "Kassenbücher"
+
 msgctxt "field:cashbook.bookcategory,name:"
 msgid "Name"
 msgstr "Name"
@@ -78,6 +82,10 @@ msgctxt "field:cashbook.bookcategory,right:"
 msgid "Right"
 msgstr "Rechts"
 
+msgctxt "field:cashbook.bookcategory,cashbooks:"
+msgid "Cashbooks"
+msgstr "Kassenbücher"
+
 
 #################
 # cashbook.book #
diff --git a/locale/en.po b/locale/en.po
index 97cfcf1..7374def 100644
--- a/locale/en.po
+++ b/locale/en.po
@@ -38,6 +38,10 @@ msgctxt "view:cashbook.bookcategory:"
 msgid "General Information"
 msgstr "General Information"
 
+msgctxt "view:cashbook.bookcategory:"
+msgid "Cashbooks"
+msgstr "Cashbooks"
+
 msgctxt "field:cashbook.bookcategory,name:"
 msgid "Name"
 msgstr "Name"
@@ -62,6 +66,10 @@ msgctxt "field:cashbook.bookcategory,right:"
 msgid "Right"
 msgstr "Right"
 
+msgctxt "field:cashbook.bookcategory,cashbooks:"
+msgid "Cashbooks"
+msgstr "Cashbooks"
+
 msgctxt "view:cashbook.book:"
 msgid "Categories"
 msgstr "Categories"
diff --git a/setup.py b/setup.py
index 235b3ab..728ff37 100644
--- a/setup.py
+++ b/setup.py
@@ -67,7 +67,9 @@ setup(name='%s_%s' % (PREFIX, MODULE),
     version=info.get('version', '0.0.1'),
     description='Tryton module to add categories for cashbooks.',
     long_description=long_description,
+    long_description_content_type='text/x-rst',
     url='https://www.m-ds.de/',
+    download_url='https://scmdev.m-ds.de/Tryton/Extra/cashbook_bookcategory',
     author='martin-data services',
     author_email='service@m-ds.de',
     license='GPL-3',
diff --git a/tests/__init__.py b/tests/__init__.py
index ead6f2c..a6930ba 100644
--- a/tests/__init__.py
+++ b/tests/__init__.py
@@ -1,24 +1,26 @@
-# This file is part of Tryton.  The COPYRIGHT file at the top level of
-# this repository contains the full copyright notices and license terms.
+# -*- coding: utf-8 -*-
+# This file is part of the cashbook-module from m-ds for Tryton.
+# The COPYRIGHT file at the top level of this repository contains the
+# full copyright notices and license terms.
 
 import trytond.tests.test_tryton
 import unittest
 
-from trytond.modules.cashbook_bookcategory.tests.test_category import CategoryTestCase
+from .test_category import CategoryTestCase
 
 
 __all__ = ['suite']
 
 
-class CashbookCategoryTestCase(\
-    CategoryTestCase,\
-    ):
+class CashbookCategoryTestCase(CategoryTestCase):
     'Test cashbook module'
     module = 'cashbook_bookcategory'
 
 # end CashbookCategoryTestCase
 
+
 def suite():
     suite = trytond.tests.test_tryton.suite()
-    suite.addTests(unittest.TestLoader().loadTestsFromTestCase(CashbookCategoryTestCase))
+    suite.addTests(unittest.TestLoader().loadTestsFromTestCase(
+        CashbookCategoryTestCase))
     return suite
diff --git a/tests/test_category.py b/tests/test_category.py
index 9677d39..4bf63d5 100644
--- a/tests/test_category.py
+++ b/tests/test_category.py
@@ -3,10 +3,9 @@
 # The COPYRIGHT file at the top level of this repository contains the
 # full copyright notices and license terms.
 
-from trytond.tests.test_tryton import ModuleTestCase, with_transaction
+from trytond.tests.test_tryton import with_transaction
 from trytond.pool import Pool
 from trytond.transaction import Transaction
-from trytond.exceptions import UserError
 from trytond.modules.cashbook.tests import CashbookTestCase
 
 
@@ -22,8 +21,7 @@ class CategoryTestCase(CashbookTestCase):
 
         company = self.prep_company()
         with Transaction().set_context({
-            'company': company.id,
-            }):
+                'company': company.id}):
             categories, = BookCategory.create([{
                 'name': 'Cat 0',
                 'childs': [('create', [{
@@ -56,8 +54,7 @@ class CategoryTestCase(CashbookTestCase):
         types = self.prep_type()
         company = self.prep_company()
         with Transaction().set_context({
-            'company': company.id,
-            }):
+                'company': company.id}):
             category, = BookCategory.create([{
                 'name': 'Cat 0',
                 'childs': [('create', [{
@@ -78,6 +75,11 @@ class CategoryTestCase(CashbookTestCase):
             self.assertEqual(len(book.categories), 1)
             self.assertEqual(book.categories[0].rec_name, 'Cat 0')
 
+            self.assertEqual(len(category.cashbooks), 1)
+            self.assertEqual(
+                category.cashbooks[0].rec_name,
+                'Book 1 | 0.00 usd | Open')
+
             # replace category
             Book.write(*[
                 [book],
diff --git a/tryton.cfg b/tryton.cfg
index ba1dc2c..706d511 100644
--- a/tryton.cfg
+++ b/tryton.cfg
@@ -1,5 +1,5 @@
 [tryton]
-version=6.0.0
+version=6.0.4
 depends:
     cashbook
 xml:
diff --git a/versiondep.txt b/versiondep.txt
index e56514a..834317e 100644
--- a/versiondep.txt
+++ b/versiondep.txt
@@ -1,2 +1 @@
-cashbook;6.0.19;6.0.999;mds
-
+cashbook;6.0.28;6.0.999;mds
diff --git a/view/category_form.xml b/view/category_form.xml
index 5366dfc..2d6d58d 100644
--- a/view/category_form.xml
+++ b/view/category_form.xml
@@ -12,6 +12,9 @@ full copyright notices and license terms. -->
             <field name="parent"/>
             <field name="childs" colspan="4"/>
         </page>
+        <page string="Cashbooks" name="cashbooks" col="1">
+            <field name="cashbooks"/>
+        </page>
     </notebook>
     <field name="company" invisible="1"/>