diff --git a/3-Domain/src/main/java/abstraction/CustomSetPersistenceDecorator.java b/3-Domain/src/main/java/abstraction/CustomSetPersistenceDecorator.java
index c81d5dd..fa25ab1 100644
--- a/3-Domain/src/main/java/abstraction/CustomSetPersistenceDecorator.java
+++ b/3-Domain/src/main/java/abstraction/CustomSetPersistenceDecorator.java
@@ -1,5 +1,8 @@
 package abstraction;
 
+import datastructures.set.CustomSet;
+import datastructures.set.CustomStrictSet;
+
 import java.util.Set;
 import java.util.stream.Stream;
 
diff --git a/3-Domain/src/main/java/category/CategoryRepository.java b/3-Domain/src/main/java/category/CategoryRepository.java
index f7089b6..ac77477 100644
--- a/3-Domain/src/main/java/category/CategoryRepository.java
+++ b/3-Domain/src/main/java/category/CategoryRepository.java
@@ -1,6 +1,6 @@
 package category;
 
-import abstraction.CustomSet;
+import datastructures.set.CustomSet;
 import abstraction.CustomSetPersistenceDecorator;
 import abstraction.PersistenceAdapter;
 import exeptions.CategoryAlreadyExists;
diff --git a/3-Domain/src/main/java/link/LinkRepository.java b/3-Domain/src/main/java/link/LinkRepository.java
index 298e39e..dbd4879 100644
--- a/3-Domain/src/main/java/link/LinkRepository.java
+++ b/3-Domain/src/main/java/link/LinkRepository.java
@@ -1,6 +1,6 @@
 package link;
 
-import abstraction.CustomSet;
+import datastructures.set.CustomSet;
 import abstraction.CustomSetPersistenceDecorator;
 import abstraction.PersistenceAdapter;
 import exeptions.LinkAlreadyExists;
diff --git a/3-Domain/src/main/java/tag/TagMatcherRepository.java b/3-Domain/src/main/java/tag/TagMatcherRepository.java
index 6577cf7..51892f7 100644
--- a/3-Domain/src/main/java/tag/TagMatcherRepository.java
+++ b/3-Domain/src/main/java/tag/TagMatcherRepository.java
@@ -1,6 +1,6 @@
 package tag;
 
-import abstraction.CustomSet;
+import datastructures.set.CustomSet;
 import abstraction.CustomSetPersistenceDecorator;
 import abstraction.PersistenceAdapter;
 import exeptions.TagMatcherAlreadyExists;
diff --git a/3-Domain/src/main/java/abstraction/CustomSet.java b/4-Abstraction/src/main/java/datastructures/set/CustomSet.java
similarity index 86%
rename from 3-Domain/src/main/java/abstraction/CustomSet.java
rename to 4-Abstraction/src/main/java/datastructures/set/CustomSet.java
index 43a7fc5..af0e1f7 100644
--- a/3-Domain/src/main/java/abstraction/CustomSet.java
+++ b/4-Abstraction/src/main/java/datastructures/set/CustomSet.java
@@ -1,4 +1,4 @@
-package abstraction;
+package datastructures.set;
 
 import java.util.Set;
 import java.util.stream.Stream;
diff --git a/3-Domain/src/main/java/abstraction/CustomStrictSet.java b/4-Abstraction/src/main/java/datastructures/set/CustomStrictSet.java
similarity index 90%
rename from 3-Domain/src/main/java/abstraction/CustomStrictSet.java
rename to 4-Abstraction/src/main/java/datastructures/set/CustomStrictSet.java
index e67c5ab..017bf88 100644
--- a/3-Domain/src/main/java/abstraction/CustomStrictSet.java
+++ b/4-Abstraction/src/main/java/datastructures/set/CustomStrictSet.java
@@ -1,7 +1,4 @@
-package abstraction;
-
-import exeptions.ElementAlreadyInSet;
-import exeptions.ElementNotInSet;
+package datastructures.set;
 
 import java.util.Set;
 import java.util.stream.Stream;
diff --git a/3-Domain/src/main/java/exeptions/ElementAlreadyInSet.java b/4-Abstraction/src/main/java/datastructures/set/ElementAlreadyInSet.java
similarity index 82%
rename from 3-Domain/src/main/java/exeptions/ElementAlreadyInSet.java
rename to 4-Abstraction/src/main/java/datastructures/set/ElementAlreadyInSet.java
index 894dcc9..3cc17f0 100644
--- a/3-Domain/src/main/java/exeptions/ElementAlreadyInSet.java
+++ b/4-Abstraction/src/main/java/datastructures/set/ElementAlreadyInSet.java
@@ -1,4 +1,4 @@
-package exeptions;
+package datastructures.set;
 
 public class ElementAlreadyInSet extends RuntimeException {
 
diff --git a/3-Domain/src/main/java/exeptions/ElementNotInSet.java b/4-Abstraction/src/main/java/datastructures/set/ElementNotInSet.java
similarity index 81%
rename from 3-Domain/src/main/java/exeptions/ElementNotInSet.java
rename to 4-Abstraction/src/main/java/datastructures/set/ElementNotInSet.java
index 19faf2a..92b9ce2 100644
--- a/3-Domain/src/main/java/exeptions/ElementNotInSet.java
+++ b/4-Abstraction/src/main/java/datastructures/set/ElementNotInSet.java
@@ -1,4 +1,4 @@
-package exeptions;
+package datastructures.set;
 
 public class ElementNotInSet extends RuntimeException {
 
diff --git a/Documentation/programmEntwurf.org b/Documentation/programmEntwurf.org
index 07dad67..b45dc69 100644
--- a/Documentation/programmEntwurf.org
+++ b/Documentation/programmEntwurf.org
@@ -345,6 +345,14 @@ kann/hier nicht sinnvoll ist]
 /[jeweils 1 Code-Beispiel zu 2 Code Smells aus der Vorlesung; jeweils
 Code-Beispiel und einen möglichen Lösungsweg bzw. den genommen
 Lösungsweg beschreiben (inkl./ /(Pseudo-)Code)]/
+**** Duplicated Code
+Da es bei Java keine Funktion zum durchsuchen eines Sets gibt wurde an mehreren Stellen ein Konstrukt, wie unten sichtbar
+verwendert.
+#+begin_src java
+public Optional<Category> getByName(CategoryName name) {
+		return categories.stream().filter(category -> category.getName().equals(name)).findFirst();
+}
+#+end_src
 
 *** 2 Refactorings
     :PROPERTIES: