diff --git a/Sources/Persistance/Persistance.cs b/Sources/Persistance/Persistance.cs
index 107af76..7e8607a 100644
--- a/Sources/Persistance/Persistance.cs
+++ b/Sources/Persistance/Persistance.cs
@@ -26,10 +26,10 @@ namespace StimPersistance
             using (XmlWriter writer = XmlWriter.Create(tw, settings)) serializer.WriteObject(writer, games);
         }
 
-        public void SaveUser(List<User> users)
+        public void SaveUser(HashSet<User> users)
         {
             XmlWriterSettings settings = new() { Indent = true };
-            DataContractSerializer serializer = new(typeof(List<User>));
+            DataContractSerializer serializer = new(typeof(HashSet<User>));
 
             using (TextWriter tw = File.CreateText("users.xml"))
             using (XmlWriter writer = XmlWriter.Create(tw, settings)) serializer.WriteObject(writer, users);
@@ -45,12 +45,12 @@ namespace StimPersistance
             return new();
         }
 
-        public List<User> LoadUser()
+        public HashSet<User> LoadUser()
         {
             if (File.Exists("users.xml"))
             {
-                DataContractSerializer serializer = new(typeof(List<User>));
-                using (Stream stream = File.OpenRead("users.xml")) return serializer.ReadObject(stream) as List<User>;
+                DataContractSerializer serializer = new(typeof(HashSet<User>));
+                using (Stream stream = File.OpenRead("users.xml")) return serializer.ReadObject(stream) as HashSet<User>;
             }
             return new();
         }        
diff --git a/Sources/Stim.Model/IPersistance.cs b/Sources/Stim.Model/IPersistance.cs
index 0717c75..36e784f 100644
--- a/Sources/Stim.Model/IPersistance.cs
+++ b/Sources/Stim.Model/IPersistance.cs
@@ -5,9 +5,9 @@ namespace Model
     public interface IPersistance
     {
         public void SaveGame(ObservableCollection<Game> games);
-        public void SaveUser(List<User> users);
+        public void SaveUser(HashSet<User> users);
         public ObservableCollection<Game> LoadGame();
-        public List<User> LoadUser();
+        public HashSet<User> LoadUser();
 
     }
 }
diff --git a/Sources/Stim.Model/Manager.cs b/Sources/Stim.Model/Manager.cs
index 906f152..0c751a7 100644
--- a/Sources/Stim.Model/Manager.cs
+++ b/Sources/Stim.Model/Manager.cs
@@ -1,4 +1,5 @@
 using System.Collections.ObjectModel;
+using System.Linq;
 
 namespace Model
 {
@@ -13,7 +14,7 @@ namespace Model
         public ObservableCollection<Game> GameList { get;}
         public ObservableCollection<Game> ResearchedGame { get; set; }
         public User CurrentUser { get; set; }
-        public List<User> Users { get; set; }
+        public HashSet<User> Users { get; set; }
 
         public Manager(IPersistance persistance)
         {
@@ -22,7 +23,10 @@ namespace Model
             GameList = persistance.LoadGame();
             ResearchedGame = persistance.LoadGame();
             Users = persistance.LoadUser();
-            if (GameList == null) { GameList = new ObservableCollection<Game>();}
+            if (GameList == null) 
+            {
+                GameList = new ObservableCollection<Game>();
+            }
         }
 
         public void AddGametoGamesList(Game game)
diff --git a/Sources/Stim.Model/User.cs b/Sources/Stim.Model/User.cs
index 5355e36..faac0bf 100644
--- a/Sources/Stim.Model/User.cs
+++ b/Sources/Stim.Model/User.cs
@@ -97,6 +97,10 @@ namespace Model
             if (string.IsNullOrWhiteSpace(Username)) return false;
             return other != null && Username.Equals(other.Username);
         }
+        public override int GetHashCode()
+        {
+            return Username.GetHashCode();
+        }
 
         public void AddReview(Game game, float rate, string text)
         {
diff --git a/Sources/Stub/Stub.cs b/Sources/Stub/Stub.cs
index 1ebfa0e..2bfa2fa 100644
--- a/Sources/Stub/Stub.cs
+++ b/Sources/Stub/Stub.cs
@@ -43,14 +43,14 @@ namespace StimStub
             return tmp;
         }
 
-        public void SaveUser(List<User> users)
+        public void SaveUser(HashSet<User> users)
         {
             foreach (User user in users) if (!users.Contains(user)) users.Add(user);
         }
 
-        public List<User> LoadUser()
+        public HashSet<User> LoadUser()
         {
-            List<User> tmp = new();
+            HashSet<User> tmp = new();
 
             return tmp;
         }