diff --git a/go.mod b/go.mod
index b15cdd7..96afcb7 100644
--- a/go.mod
+++ b/go.mod
@@ -1,6 +1,6 @@
 module git.fsdpf.net/go/contracts
 
-go 1.18
+go 1.21
 
 require (
 	git.fsdpf.net/go/db v0.0.0-20230621051209-5740d112407f
diff --git a/support/list.go b/support/list.go
index ed7f002..856fe3b 100644
--- a/support/list.go
+++ b/support/list.go
@@ -5,6 +5,7 @@ import (
 	"reflect"
 
 	"git.fsdpf.net/go/contracts"
+	"github.com/samber/lo"
 	"github.com/spf13/cast"
 )
 
@@ -36,7 +37,7 @@ func (this *OperationAccess) Push(k string, input ...any) error {
 	for i := 0; i < len(input); i++ {
 		if v, err := this.Convert(input[i]); err != nil {
 			return err
-		} else {
+		} else if !lo.Contains(this.data[k], v) {
 			this.data[k] = append(this.data[k], v)
 		}
 	}
@@ -44,6 +45,13 @@ func (this *OperationAccess) Push(k string, input ...any) error {
 	return nil
 }
 
+func (this OperationAccess) Merge(item OperationAccess) error {
+	for k, v := range item.data {
+		this.Push(k, v...)
+	}
+	return nil
+}
+
 func (this OperationAccess) Convert(v any) (any, error) {
 	if this.typ == reflect.Int {
 		return cast.ToIntE(v)
@@ -64,13 +72,7 @@ func (this OperationAccess) Exist(k string, v any) bool {
 		return false
 	}
 
-	for i := 0; i < len(items); i++ {
-		if items[i] == flag {
-			return true
-		}
-	}
-
-	return false
+	return lo.Contains(items, flag)
 }
 
 func (this OperationAccess) MarshalJSON() ([]byte, error) {