diff --git a/Aufgaben/DuplicateCheckerLib/DuplicateCheckerLib.dll b/Aufgaben/DuplicateCheckerLib/DuplicateCheckerLib.dll
new file mode 100644
index 0000000..10ce845
Binary files /dev/null and b/Aufgaben/DuplicateCheckerLib/DuplicateCheckerLib.dll differ
diff --git a/Aufgaben/DuplicateCheckerLib/DuplicateCheckerLib/DuplicateCheckerLib.sln b/Aufgaben/DuplicateCheckerLib/DuplicateCheckerLib/DuplicateCheckerLib.sln
new file mode 100644
index 0000000..c997fd2
--- /dev/null
+++ b/Aufgaben/DuplicateCheckerLib/DuplicateCheckerLib/DuplicateCheckerLib.sln
@@ -0,0 +1,25 @@
+
+Microsoft Visual Studio Solution File, Format Version 12.00
+# Visual Studio Version 16
+VisualStudioVersion = 16.0.28803.352
+MinimumVisualStudioVersion = 10.0.40219.1
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "DuplicateCheckerLib", "DuplicateCheckerLib\DuplicateCheckerLib.csproj", "{17DFFFC5-D41F-4C9B-99AD-3A14920152DB}"
+EndProject
+Global
+	GlobalSection(SolutionConfigurationPlatforms) = preSolution
+		Debug|Any CPU = Debug|Any CPU
+		Release|Any CPU = Release|Any CPU
+	EndGlobalSection
+	GlobalSection(ProjectConfigurationPlatforms) = postSolution
+		{17DFFFC5-D41F-4C9B-99AD-3A14920152DB}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{17DFFFC5-D41F-4C9B-99AD-3A14920152DB}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{17DFFFC5-D41F-4C9B-99AD-3A14920152DB}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{17DFFFC5-D41F-4C9B-99AD-3A14920152DB}.Release|Any CPU.Build.0 = Release|Any CPU
+	EndGlobalSection
+	GlobalSection(SolutionProperties) = preSolution
+		HideSolutionNode = FALSE
+	EndGlobalSection
+	GlobalSection(ExtensibilityGlobals) = postSolution
+		SolutionGuid = {A67D4C42-99C6-4966-8AAB-083C0B66A643}
+	EndGlobalSection
+EndGlobal
diff --git a/Aufgaben/DuplicateCheckerLib/DuplicateCheckerLib/DuplicateCheckerLib/DuplicateChecker.cs b/Aufgaben/DuplicateCheckerLib/DuplicateCheckerLib/DuplicateCheckerLib/DuplicateChecker.cs
new file mode 100644
index 0000000..ece07f6
--- /dev/null
+++ b/Aufgaben/DuplicateCheckerLib/DuplicateCheckerLib/DuplicateCheckerLib/DuplicateChecker.cs
@@ -0,0 +1,17 @@
+using System.Collections.Generic;
+
+namespace DuplicateCheckerLib {
+    public class DuplicateChecker {
+        public IEnumerable<IEntity> FindDuplicates(IEnumerable<IEntity> list) {
+            var hashSet = new HashSet<IEntity>();
+            var ret = new List<IEntity>();
+            foreach (var item in list) {
+                if (!hashSet.Add(item)) {
+                    ret.Add(item);
+                }
+            }
+
+            return ret;
+        }
+    }
+}
diff --git a/Aufgaben/DuplicateCheckerLib/DuplicateCheckerLib/DuplicateCheckerLib/DuplicateCheckerLib.csproj b/Aufgaben/DuplicateCheckerLib/DuplicateCheckerLib/DuplicateCheckerLib/DuplicateCheckerLib.csproj
new file mode 100644
index 0000000..72764a6
--- /dev/null
+++ b/Aufgaben/DuplicateCheckerLib/DuplicateCheckerLib/DuplicateCheckerLib/DuplicateCheckerLib.csproj
@@ -0,0 +1,7 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <TargetFramework>netstandard2.0</TargetFramework>
+  </PropertyGroup>
+
+</Project>
diff --git a/Aufgaben/DuplicateCheckerLib/DuplicateCheckerLib/DuplicateCheckerLib/IEntity.cs b/Aufgaben/DuplicateCheckerLib/DuplicateCheckerLib/DuplicateCheckerLib/IEntity.cs
new file mode 100644
index 0000000..f44e215
--- /dev/null
+++ b/Aufgaben/DuplicateCheckerLib/DuplicateCheckerLib/DuplicateCheckerLib/IEntity.cs
@@ -0,0 +1,8 @@
+using System;
+using System.Collections.Generic;
+using System.Text;
+
+namespace DuplicateCheckerLib {
+    public interface IEntity {
+    }
+}
diff --git a/Generics/Generics.pdf b/Aufgaben/Generics.pdf
similarity index 100%
rename from Generics/Generics.pdf
rename to Aufgaben/Generics.pdf
diff --git a/Generics/IRepositoryBase.cs b/Aufgaben/IRepositoryBase.cs
similarity index 100%
rename from Generics/IRepositoryBase.cs
rename to Aufgaben/IRepositoryBase.cs
diff --git a/InversionOfControl/InversionOfControl.pdf b/Aufgaben/InversionOfControl.pdf
similarity index 100%
rename from InversionOfControl/InversionOfControl.pdf
rename to Aufgaben/InversionOfControl.pdf
diff --git a/LINQ/LINQ_LinqToSql.pdf b/Aufgaben/LINQ_LinqToSql.pdf
similarity index 100%
rename from LINQ/LINQ_LinqToSql.pdf
rename to Aufgaben/LINQ_LinqToSql.pdf
diff --git a/NuGet/NuGet.pdf b/Aufgaben/NuGet.pdf
similarity index 100%
rename from NuGet/NuGet.pdf
rename to Aufgaben/NuGet.pdf
diff --git a/ObjectEquality/Object Equality.pdf b/Aufgaben/Object Equality.pdf
similarity index 100%
rename from ObjectEquality/Object Equality.pdf
rename to Aufgaben/Object Equality.pdf
diff --git a/Reflection_Serialization/Reflection_Serialization.pdf b/Aufgaben/Reflection_Serialization.pdf
similarity index 100%
rename from Reflection_Serialization/Reflection_Serialization.pdf
rename to Aufgaben/Reflection_Serialization.pdf
diff --git a/RegEx/RegEx.pdf b/Aufgaben/RegEx.pdf
similarity index 100%
rename from RegEx/RegEx.pdf
rename to Aufgaben/RegEx.pdf
diff --git a/ObjectEquality/DuplicateCheckerLib.zip b/ObjectEquality/DuplicateCheckerLib.zip
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index 24e9537..0000000
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