diff --git a/filter/filter.go b/filter/filter.go
index 7b2d92b..4d535aa 100644
--- a/filter/filter.go
+++ b/filter/filter.go
@@ -16,36 +16,7 @@ limitations under the License.
 
 package filter
 
-import (
-	"fmt"
-	"strings"
-)
-
-// Number combines the primitives generally considered numbers by JSON
-// and other high-level structure data representations.
-type Number interface {
-	int16 | int32 | int64 | float32 | float64
-}
-
-// Text combines byte slice and string.
-type Text interface {
-	[]byte | string
-}
-
-// P is for "principle" in this case. These are the types that have
-// representations in JSON and other high-level structured data
-// representations.
-type P interface {
-	int16 | int32 | int64 | float32 | float64 |
-		[]byte | string | bool
-}
-
-// Println prints ever element of the set.
-func Println[T P](set []T) {
-	for _, i := range set {
-		fmt.Println(i)
-	}
-}
+import "strings"
 
 // HasPrefix filters the Text input set and returns only those elements
 // that have the give prefix.
diff --git a/filter/filter_test.go b/filter/filter_test.go
index 93a7a1c..47ff4bc 100644
--- a/filter/filter_test.go
+++ b/filter/filter_test.go
@@ -39,17 +39,3 @@ func ExampleMinus() {
 	// Output:
 	// [one three five seven]
 }
-
-func ExamplePrintln() {
-	set := []string{"doe", "ray", "mi"}
-	filter.Println(set)
-	bools := []bool{false, true, true}
-	filter.Println(bools)
-	// Output:
-	// doe
-	// ray
-	// mi
-	// false
-	// true
-	// true
-}
diff --git a/filter/map.go b/filter/map.go
new file mode 100644
index 0000000..90e8870
--- /dev/null
+++ b/filter/map.go
@@ -0,0 +1,26 @@
+/*
+Copyright 2022 Robert S. Muhlestein.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package filter
+
+import "fmt"
+
+// Println prints ever element of the set.
+func Println[T P](set []T) {
+	for _, i := range set {
+		fmt.Println(i)
+	}
+}
diff --git a/filter/map_test.go b/filter/map_test.go
new file mode 100644
index 0000000..2540863
--- /dev/null
+++ b/filter/map_test.go
@@ -0,0 +1,17 @@
+package filter_test
+
+import "github.com/rwxrob/bonzai/filter"
+
+func ExamplePrintln() {
+	set := []string{"doe", "ray", "mi"}
+	filter.Println(set)
+	bools := []bool{false, true, true}
+	filter.Println(bools)
+	// Output:
+	// doe
+	// ray
+	// mi
+	// false
+	// true
+	// true
+}
diff --git a/filter/types.go b/filter/types.go
new file mode 100644
index 0000000..5fa0f9d
--- /dev/null
+++ b/filter/types.go
@@ -0,0 +1,36 @@
+/*
+Copyright 2022 Robert S. Muhlestein.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package filter
+
+// Number combines the primitives generally considered numbers by JSON
+// and other high-level structure data representations.
+type Number interface {
+	int16 | int32 | int64 | float32 | float64
+}
+
+// Text combines byte slice and string.
+type Text interface {
+	[]byte | string
+}
+
+// P is for "principle" in this case. These are the types that have
+// representations in JSON and other high-level structured data
+// representations.
+type P interface {
+	int16 | int32 | int64 | float32 | float64 |
+		[]byte | string | bool
+}