diff --git a/requirements.txt b/requirements.txt
index 67c906c..fac96a0 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -1,11 +1,11 @@
-outdated
-lxml
-pint
-beautifulsoup4
-tabulate
-path
-shapely
-numpy
-matplotlib
-pandas==1.2.2  # because of io.common methods
-sympy==1.5.1  # because of specific expression parsing
\ No newline at end of file
+outdated~=0.2.1
+pint~=0.16.1
+tabulate~=0.8.9
+path~=15.1.2
+shapely~=1.7.1
+numpy~=1.20.1
+matplotlib~=3.3.4
+pandas~=1.2.2  # because of io.common methods
+sympy~=1.5.1  # because of specific expression parsing
+beautifulsoup4~=4.9.3
+lxml~=4.6.3
\ No newline at end of file
diff --git a/trnsystor/__init__.py b/trnsystor/__init__.py
index d3e449b..bda4bc8 100644
--- a/trnsystor/__init__.py
+++ b/trnsystor/__init__.py
@@ -2,14 +2,29 @@
 
 from outdated import warn_if_outdated
 
+from .collections import EquationCollection
 from .controlcards import ControlCards
 from .deck import Deck
+from .statement import Equation
 from .trnsysmodel import TrnsysModel
 
 # Version of the package
-__version__ = "1.3.2"
+from pkg_resources import get_distribution, DistributionNotFound
 
-# warn if a newer version of archetypal is available
-warn_if_outdated("trnsystor", __version__)
+try:
+    __version__ = get_distribution("archetypal").version
+except DistributionNotFound:
+    # package is not installed
+    __version__ = "0.0.0"  # should happen only if package is copied, not installed.
+else:
+    # warn if a newer version of trnsystor is available
+    from outdated import warn_if_outdated
 
-__all__ = ["ControlCards", "Deck", "TrnsysModel", "__version__"]
+__all__ = [
+    "Equation",
+    "EquationCollection",
+    "ControlCards",
+    "Deck",
+    "TrnsysModel",
+    "__version__",
+]