diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index e757848..a48a77e 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -232,7 +232,7 @@ See also the next section.
 
 These suggestions apply to the development of any Concourse resource.
 
-### Building a new image and ensuring that the pipeline picks it up 
+### Building a new image and ensuring that the pipeline picks it up
 
 After the local tests are passing, the quickest way to test in a pipeline the freshly pushed version of the Docker image used to be the `fly check-resource-type` command. Unfortunately somewhere in the Concourse 7.6.x series this broke (details: [registry-image-resource #316](https://github.com/concourse/registry-image-resource/issues/316)).
 
@@ -248,7 +248,7 @@ You can follow two steps:
 1. `fly set-pipeline` with a check_interval for the resource type of 1m instead of the recommended 24h.
 2. `fly clear-version`.
 
-For example, assuming that the test pipeline is called `cogito-test`, that the resource in the pipeline is called `cogito` and that there is a job called `motormouse` (all this is true by using the sample pipeline [pipelines/cogito.yml](./pipelines/cogito.yml)), 
+For example, assuming that the test pipeline is called `cogito-test`, that the resource in the pipeline is called `cogito` and that there is a job called `motormouse` (all this is true by using the sample pipeline [pipelines/cogito.yml](./pipelines/cogito.yml)).
 
 Step 1:
 
@@ -268,7 +268,7 @@ Step 2 (the sleep is fundamental to let check_every expire):
 ```
 $ task test:all docker:build docker:smoke docker:push &&
   fly -t cogito clear-versions --resource-type=cogito-test/cogito &&
-  echo "sleeping and hoping :-(" && 
+  echo "sleeping and hoping :-(" &&
   sleep 70 &&
   fly -t cogito trigger-job -j cogito-test/motormouse -w
 ```
@@ -336,7 +336,7 @@ Update the expired secrets as follows.
 ## Regenerate your GitHub personal access token (PAT)
 
 1. Go to [Settings | Tokens](https://github.com/settings/tokens) for your account.
-2. Create or regenerate a token with name `test-cogito`, with scope "repo:status". Set an expiration of 90 days.
+2. Create or regenerate a token with name `test-cogito`, with scope `repo:status`. Set an expiration of 90 days.
 3. Copy the token.
 
 ## Regenerate a Google Chat hook
diff --git a/sets/sets.go b/sets/sets.go
index 3c892f8..658b407 100644
--- a/sets/sets.go
+++ b/sets/sets.go
@@ -105,3 +105,15 @@ func (s *Set[T]) Intersection(x *Set[T]) *Set[T] {
 	}
 	return result
 }
+
+// Union returns a set containing all the elements of s and x.
+func (s *Set[T]) Union(x *Set[T]) *Set[T] {
+	result := New[T](max(s.Size(), x.Size()))
+	for item := range s.items {
+		result.items[item] = struct{}{}
+	}
+	for item := range x.items {
+		result.items[item] = struct{}{}
+	}
+	return result
+}
diff --git a/sets/sets_test.go b/sets/sets_test.go
index 32c3fa5..9f3cfc0 100644
--- a/sets/sets_test.go
+++ b/sets/sets_test.go
@@ -201,6 +201,65 @@ func TestIntersection(t *testing.T) {
 	}
 }
 
+func TestUnion(t *testing.T) {
+	type testCase struct {
+		name     string
+		s        *sets.Set[int]
+		x        *sets.Set[int]
+		wantList []int
+	}
+
+	test := func(t *testing.T, tc testCase) {
+		result := tc.s.Union(tc.x)
+		sorted := result.OrderedList()
+
+		qt.Assert(t, qt.DeepEquals(sorted, tc.wantList))
+	}
+
+	testCases := []testCase{
+		{
+			name:     "both empty",
+			s:        sets.From[int](),
+			x:        sets.From[int](),
+			wantList: []int{},
+		},
+		{
+			name:     "empty x",
+			s:        sets.From(1, 2),
+			x:        sets.From[int](),
+			wantList: []int{1, 2},
+		},
+		{
+			name:     "empty s",
+			s:        sets.From[int](),
+			x:        sets.From(1, 2),
+			wantList: []int{1, 2},
+		},
+		{
+			name:     "identical",
+			s:        sets.From(1, 2),
+			x:        sets.From(1, 2),
+			wantList: []int{1, 2},
+		},
+		{
+			name:     "all different",
+			s:        sets.From(1, 3),
+			x:        sets.From(2, 4),
+			wantList: []int{1, 2, 3, 4},
+		},
+		{
+			name:     "partial overlap",
+			s:        sets.From(1, 3),
+			x:        sets.From(3, 5),
+			wantList: []int{1, 3, 5},
+		},
+	}
+
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) { test(t, tc) })
+	}
+}
+
 func TestRemoveFound(t *testing.T) {
 	type testCase struct {
 		name     string