diff --git a/src/random_events/__init__.py b/src/random_events/__init__.py
index 668c344..e7c12d2 100644
--- a/src/random_events/__init__.py
+++ b/src/random_events/__init__.py
@@ -1 +1 @@
-__version__ = '2.0.2'
+__version__ = '2.0.3'
diff --git a/src/random_events/events.py b/src/random_events/events.py
index 3914eba..e0e7bb3 100644
--- a/src/random_events/events.py
+++ b/src/random_events/events.py
@@ -7,7 +7,7 @@
 import portion
 import plotly.graph_objects as go
 
-from typing_extensions import Set, Union, Any, TYPE_CHECKING, Iterable, List, Self, Dict
+from typing_extensions import Set, Union, Any, TYPE_CHECKING, Iterable, List, Self, Dict, Tuple
 
 from .variables import Variable, Continuous, Discrete
 
@@ -173,7 +173,7 @@ def union(self, other: EventType) -> ComplexEvent:
 
         # add the fragments of the other event
         complex_self.events.extend(fragments_of_other.events)
-        return complex_self
+        return ComplexEvent(complex_self.events)
 
     def difference(self, other: EventType) -> ComplexEvent:
         # if the other is a complex event
@@ -413,6 +413,14 @@ def plotly_layout(self) -> Dict:
     def __hash__(self):
         return hash(tuple(sorted(self.items())))
 
+    def fill_missing_variables(self, variables: Iterable[Variable]):
+        """
+        Fill missing variables with their entire domain.
+        """
+        for variable in variables:
+            if variable not in self:
+                self[variable] = variable.domain
+
 
 class EncodedEvent(Event):
     """
@@ -457,6 +465,11 @@ def decode(self) -> Event:
         """
         return Event({variable: variable.decode_many(value) for variable, value in self.items()})
 
+    def fill_missing_variables(self, variables: Iterable[Variable]):
+        for variable in variables:
+            if variable not in self:
+                self[variable] = variable.encode_many(variable.domain)
+
 
 class ComplexEvent(SupportsSetOperations):
     """
@@ -466,8 +479,20 @@ class ComplexEvent(SupportsSetOperations):
 
     def __init__(self, events: Iterable[Event]):
         self.events = list(event for event in events if not event.is_empty())
+        variables = self.variables
+        for event in self.events:
+            event.fill_missing_variables(variables)
 
-    def union(self, other: Self) -> Self:
+    @property
+    def variables(self) -> Tuple[Variable, ...]:
+        """
+        Get the variables of the complex event.
+        """
+        return tuple(sorted(set(variable for event in self.events for variable in event.keys())))
+
+    def union(self, other: EventType) -> Self:
+        if isinstance(other, Event):
+            return self.union(ComplexEvent([other]))
         result = ComplexEvent(self.events + other.events)
         return result.make_events_disjoint().simplify()
 
@@ -573,11 +598,15 @@ def simplify(self) -> Self:
         # if no simplification is possible, return the current complex event
         return self.__copy__()
 
-    def intersection(self, other: Self) -> Self:
+    def intersection(self, other: EventType) -> Self:
+        if isinstance(other, Event):
+            return self.intersection(ComplexEvent([other]))
         intersections = [event.intersection(other_event) for other_event in other.events for event in self.events]
         return ComplexEvent(intersections)
 
-    def difference(self, other: Self) -> Self:
+    def difference(self, other: EventType) -> Self:
+        if isinstance(other, Event):
+            return self.difference(ComplexEvent([other]))
         return self.intersection(other.complement())
 
     def complement(self) -> Self:
@@ -632,4 +661,4 @@ def is_empty(self) -> bool:
         return len(self.events) == 0
 
 
-EventType = Union[Event, EncodedEvent, ComplexEvent]
\ No newline at end of file
+EventType = Union[Event, EncodedEvent, ComplexEvent]
diff --git a/test/test_events.py b/test/test_events.py
index 848d6c6..21adfce 100644
--- a/test/test_events.py
+++ b/test/test_events.py
@@ -352,6 +352,20 @@ def test_chained_complement(self):
         self.assertEqual(len(copied_event.events), 1)
         self.assertEqual(copied_event.events[0], event)
 
+    def test_union_of_simple_with_complex(self):
+        event = Event({self.x: portion.closed(0, 1), self.y: portion.closed(0, 1)})
+        complex_event = ComplexEvent([event])
+        union1 = event.union(complex_event)
+        union2 = complex_event.union(event)
+        self.assertEqual(union1, union2)
+
+    def test_union_with_different_variables(self):
+        event1 = Event({self.x: portion.closed(0, 1)})
+        event2 = Event({self.y: portion.closed(0, 1)})
+        union = event1.union(event2)
+        for event in union.events:
+            self.assertEqual(len(event), 2)
+
 
 class PlottingTestCase(unittest.TestCase):
     x: Continuous = Continuous("x")