diff --git a/README.md b/README.md
index 8a4bb95..f3cdcfa 100644
--- a/README.md
+++ b/README.md
@@ -1,2 +1,11 @@
-pylib
-=====
+# Install
+
+Install in "development mode" so any changes of the program is effective.
+
+    git clone http://weseng.de/daniel/pylib.git
+    cd pylib
+    pip install --user -e .
+
+# Uninstall
+
+    pip uninstall pylib
diff --git a/pylib/__init__.py b/pylib/__init__.py
deleted file mode 100644
index e946c39..0000000
--- a/pylib/__init__.py
+++ /dev/null
@@ -1,13 +0,0 @@
-import os
-import sys
-
-# Add vendor directory to module search path
-project_dir = os.path.abspath(os.path.dirname(__file__))
-parent_dir = os.path.dirname(project_dir)
-vendor_dir = os.path.join(parent_dir, 'vendor')
-
-if vendor_dir not in sys.path:
-  sys.path.append(vendor_dir)
-
-# Now you can import any library located in the "vendor" folder!
-# import drawille
diff --git a/setup.py b/setup.py
new file mode 100644
index 0000000..851dd6b
--- /dev/null
+++ b/setup.py
@@ -0,0 +1,35 @@
+#!/usr/bin/env python
+# -*- coding: utf-8 -*-
+from os.path import join, dirname
+from setuptools import setup, find_packages
+
+# Utility function to read the README file. Used for the long_description.
+def read(fname):
+  with open(join(dirname(__file__), fname)) as fh:
+    return fh.read()
+
+setup(
+  name="pylib",
+  version="2021.02.01",
+  description="python library",
+  long_description=read("README.md"),
+  author="Daniel Weschke",
+  author_email="daniel.weschke@directbox.de",
+  package_dir={'': 'src'},
+  packages=find_packages("src"),
+  keywords = ['data', 'date', 'draw', 'geometry', 'mathematics', 'numerical', 'time'],
+  license="MIT",
+  classifiers=[
+    'Environment :: Console',
+    'Intended Audience :: Education',
+    'Intended Audience :: End Users/Desktop',
+    'Intended Audience :: Developers',
+    'Intended Audience :: Science/Research',
+    'License :: OSI Approved :: MIT License',
+    'Natural Language :: English',
+    'Operating System :: OS Independent',
+    'Programming Language :: Python',
+    'Topic :: Scientific/Engineering',
+    'Topic :: Scientific/Engineering :: Physics'
+  ]
+)
diff --git a/src/pylib/__init__.py b/src/pylib/__init__.py
new file mode 100644
index 0000000..e71b082
--- /dev/null
+++ b/src/pylib/__init__.py
@@ -0,0 +1,13 @@
+import os
+import sys
+
+# Add vendor directory to module search path
+_project_dir = os.path.abspath(os.path.dirname(__file__))
+_parent_dir = os.path.dirname(_project_dir)
+_vendor_dir = os.path.join(_parent_dir, 'vendor')
+
+if _vendor_dir not in sys.path:
+  sys.path.append(_vendor_dir)
+
+# Now you can import any library located in the "vendor" folder!
+# import drawille
diff --git a/pylib/data.py b/src/pylib/data.py
similarity index 100%
rename from pylib/data.py
rename to src/pylib/data.py
diff --git a/pylib/data_step.py b/src/pylib/data_step.py
similarity index 100%
rename from pylib/data_step.py
rename to src/pylib/data_step.py
diff --git a/pylib/data_step_std.py b/src/pylib/data_step_std.py
similarity index 100%
rename from pylib/data_step_std.py
rename to src/pylib/data_step_std.py
diff --git a/pylib/date.py b/src/pylib/date.py
similarity index 54%
rename from pylib/date.py
rename to src/pylib/date.py
index 4cf20be..ce923b6 100644
--- a/pylib/date.py
+++ b/src/pylib/date.py
@@ -10,16 +10,58 @@
    
 .. moduleauthor:: Daniel Weschke <daniel.weschke@directbox.de>
 """
+import datetime
 
+def computus_anonymous_gregorian(year):
+  """Computus anonymous Gregorian algorithm or Meeus/Jones/Butcher
+  algorithm.
+
+  :param year: the year to calculate the Easter Sunday
+  :type year: int
+
+  :returns: the day of Easter Sunday
+  :rtype: datetime.date
+
+  For Gregorian calendar (1583 and onward)
+  Works without exeptions.
+
+  Published
+  1876 by Anonymous in Nature
+  1877 by Samuel Butcher in The Ecclesiastical Calendar
+  1916 by Arthur Downing in The Observatory
+  1922 by Harold Spencer Jones in General Astronomy
+  1988 by Peter Duffett-Smith in Practical Astronomy with your Calculator
+  1991 by Jean Meeus in Astronomical Algorithms
+
+  source: https://de.wikipedia.org/wiki/Spencers_Osterformel
+  source: https://en.wikipedia.org/wiki/Computus#Anonymous_Gregorian_algorithm
+  """
+  a = year % 19
+  b = year // 100
+  c = year % 100
+  d = b // 4
+  e = b % 4
+  f = (b + 8) // 25
+  g = (b - f + 1) // 3
+  h = (19 * a + b - d - g + 15) % 30
+  i = c // 4
+  k = c % 4
+  l = (32 + 2 * e + 2 * i - h - k) % 7
+  m = (a + 11 * h + 22 * l) // 451
+  n = (h + l - 7 * m + 114) // 31
+  o = (h + l - 7 * m + 114) % 31
+  return datetime.date(year, n, o + 1)
+
+# was not correct for 2020
 def gaußsche_osterformel(year):
   """Gaußsche Osterformel.
 
   :param year: the year to calculate the Easter Sunday
   :type year: int
-  
-  :returns: the day of Easter Sunday as a day in march.
-  :rtype: int
-  
+
+  :returns: the day of Easter Sunday (computed as a day in march).
+  :rtype: datetime.date
+
   :ivar X: Das Jahr / year
   :vartype X: int
   :ivar K(X): Die Säkularzahl
@@ -42,7 +84,7 @@ def gaußsche_osterformel(year):
   :vartype OE(OG,SZ): int
   :ivar OS(OG,OE): Das Datum des Ostersonntags als Märzdatum (32. März = 1. April usw.)
   :vartype OS(OG,OE): int
-  
+
   Algorithmus gilt für den Gregorianischen Kalender.
 
   source: https://de.wikipedia.org/wiki/Gau%C3%9Fsche_Osterformel
@@ -58,30 +100,29 @@ def gaußsche_osterformel(year):
   sz = 7 - (x + x // 4 + s) % 7
   oe = 7 - (og - sz) % 7
   os = og + oe
-  return os
+  
+  march = datetime.date(year, 3, 1)
+  day = march + datetime.timedelta(days=os)
+  return day
 
 def easter_sunday(year):
   """Easter Sunday.
 
   :param year: the year to calculate the Easter Sunday
   :type year: int
-  
+
   :returns: the day of Easter Sunday
   :rtype: datetime.date"""
-  import datetime
-  march = datetime.date(year, 3, 1)
-  day = march + datetime.timedelta(days=gaußsche_osterformel(year))
-  return day
+  return computus_anonymous_gregorian(year)
 
 def easter_friday(year):
   """Easter Friday.
 
   :param year: the year to calculate the Easter Friday
   :type year: int
-  
+
   :returns: the day of Easter Friday
   :rtype: datetime.date"""
-  import datetime
   day = easter_sunday(year) + datetime.timedelta(days=-2)
   return day
 
@@ -90,10 +131,9 @@ def easter_monday(year):
 
   :param year: the year to calculate the Easter Monday
   :type year: int
-  
+
   :returns: the day of Easter Monday
   :rtype: datetime.date"""
-  import datetime
   day = easter_sunday(year) + datetime.timedelta(days=+1)
   return day
 
@@ -102,10 +142,9 @@ def ascension_of_jesus(year):
 
   :param year: the year to calculate the ascension of Jesus
   :type year: int
-  
+
   :returns: the day of ascension of Jesus
   :rtype: datetime.date"""
-  import datetime
   day = easter_sunday(year) + datetime.timedelta(days=+39)
   return day
 
@@ -114,9 +153,32 @@ def pentecost(year):
 
   :param year: the year to calculate the Pentecost
   :type year: int
-  
+
   :returns: the day of Pentecost
   :rtype: datetime.date"""
-  import datetime
   day = easter_sunday(year) + datetime.timedelta(days=+49)
   return day
+
+def daylist(day, end, excludedweekdays=[], excludeddays=[], inclusive=True):
+  """Create a list of dates
+
+  :param day: the beginning day for the list
+  :type day: datetime.date
+  :param end: the end day of the list
+  :type end: datetime.date
+  :param excludedweekdays: list of days of the week to exclude, where
+    Monday == 1 and Sunday == 7 (ISO weekday, default = [])
+  :type excludedweekdays: list of int
+  :param excludeddays: list of days to exclude, e.g. vacation, sick
+    leaves, trainings (default = [])
+  :type excludedweekdays: list of datetime.date
+  :param inclusive: include the end day in the list (default = True)
+  :type inclusive: bool
+  """
+  # TODO: includeddays: e.g. work on weekend days if using excludedweekdays
+  result = []
+  while day <= end if inclusive else day < end:
+    if day.isoweekday() not in excludedweekdays and day not in excludeddays:
+      result.append(day)
+    day += datetime.timedelta(days=1)
+  return result
diff --git a/pylib/drawblock.py b/src/pylib/drawblock.py
similarity index 100%
rename from pylib/drawblock.py
rename to src/pylib/drawblock.py
diff --git a/pylib/function.py b/src/pylib/function.py
similarity index 100%
rename from pylib/function.py
rename to src/pylib/function.py
diff --git a/pylib/geometry.py b/src/pylib/geometry.py
similarity index 100%
rename from pylib/geometry.py
rename to src/pylib/geometry.py
diff --git a/pylib/geometry2d.py b/src/pylib/geometry2d.py
similarity index 100%
rename from pylib/geometry2d.py
rename to src/pylib/geometry2d.py
diff --git a/pylib/geometry2d_plot.py b/src/pylib/geometry2d_plot.py
similarity index 100%
rename from pylib/geometry2d_plot.py
rename to src/pylib/geometry2d_plot.py
diff --git a/pylib/geometry_plot.py b/src/pylib/geometry_plot.py
similarity index 100%
rename from pylib/geometry_plot.py
rename to src/pylib/geometry_plot.py
diff --git a/pylib/geometry_plot_pylab.py b/src/pylib/geometry_plot_pylab.py
similarity index 100%
rename from pylib/geometry_plot_pylab.py
rename to src/pylib/geometry_plot_pylab.py
diff --git a/pylib/helper.py b/src/pylib/helper.py
similarity index 100%
rename from pylib/helper.py
rename to src/pylib/helper.py
diff --git a/pylib/mathematics.py b/src/pylib/mathematics.py
similarity index 100%
rename from pylib/mathematics.py
rename to src/pylib/mathematics.py
diff --git a/pylib/numerical/__init__.py b/src/pylib/numerical/__init__.py
similarity index 100%
rename from pylib/numerical/__init__.py
rename to src/pylib/numerical/__init__.py
diff --git a/pylib/numerical/fit.py b/src/pylib/numerical/fit.py
similarity index 100%
rename from pylib/numerical/fit.py
rename to src/pylib/numerical/fit.py
diff --git a/pylib/numerical/integration.py b/src/pylib/numerical/integration.py
similarity index 100%
rename from pylib/numerical/integration.py
rename to src/pylib/numerical/integration.py
diff --git a/pylib/numerical/ode.py b/src/pylib/numerical/ode.py
similarity index 100%
rename from pylib/numerical/ode.py
rename to src/pylib/numerical/ode.py
diff --git a/pylib/numerical/ode_model.py b/src/pylib/numerical/ode_model.py
similarity index 100%
rename from pylib/numerical/ode_model.py
rename to src/pylib/numerical/ode_model.py
diff --git a/pylib/time_of_day.py b/src/pylib/time_of_day.py
similarity index 100%
rename from pylib/time_of_day.py
rename to src/pylib/time_of_day.py
diff --git a/pylib/tui.py b/src/pylib/tui.py
similarity index 100%
rename from pylib/tui.py
rename to src/pylib/tui.py
diff --git a/vendor/drawille.py b/src/vendor/drawille.py
similarity index 100%
rename from vendor/drawille.py
rename to src/vendor/drawille.py