diff --git a/1-Adapter/src/main/java/persistence/CSVCategoryPersistenceAdapter.java b/1-Adapter/src/main/java/persistence/CSVCategoryPersistenceAdapter.java
index ff56cd5..86dff90 100644
--- a/1-Adapter/src/main/java/persistence/CSVCategoryPersistenceAdapter.java
+++ b/1-Adapter/src/main/java/persistence/CSVCategoryPersistenceAdapter.java
@@ -1,17 +1,22 @@
 package persistence;
 
+import abstraction.PersistenceAdapter;
 import category.Category;
-import category.CategoryPersistenceAdapter;
 
 import java.util.Set;
 
-public class CSVCategoryPersistenceAdapter implements CategoryPersistenceAdapter {
+public class CSVCategoryPersistenceAdapter implements PersistenceAdapter<Category> {
 
 	@Override
 	public Set<Category> getAll() {
 		return null;
 	}
 
+	@Override
+	public Boolean remove(Category value) {
+		return null;
+	}
+
 	@Override
 	public Boolean add(Category category) {
 		return null;
diff --git a/2-Application/src/main/java/category/CategoryIdGenerator.java b/2-Application/src/main/java/category/CategoryIdGenerator.java
index 637fe15..4e22742 100644
--- a/2-Application/src/main/java/category/CategoryIdGenerator.java
+++ b/2-Application/src/main/java/category/CategoryIdGenerator.java
@@ -1,6 +1,5 @@
 package category;
 
-public interface CategoryIdGenerator
-{
+public interface CategoryIdGenerator {
 	CategoryId generateId();
 }
diff --git a/3-Domain/src/main/java/category/CategoryRepository.java b/3-Domain/src/main/java/category/CategoryRepository.java
index dde235f..a858394 100644
--- a/3-Domain/src/main/java/category/CategoryRepository.java
+++ b/3-Domain/src/main/java/category/CategoryRepository.java
@@ -1,5 +1,8 @@
 package category;
 
+import abstraction.CustomSet;
+import abstraction.PersistenceAdapter;
+import abstraction.CustomSetPersistenceDecorator;
 import exeptions.CategoryAlreadyExists;
 import exeptions.NonUniqueId;
 
@@ -8,12 +11,11 @@ import java.util.Set;
 
 public class CategoryRepository {
 
-	final private CategoryPersistenceAdapter categoryPersistenceAdapter;
-	final private Set<Category> categories;
 
-	public CategoryRepository(CategoryPersistenceAdapter categoryPersistenceAdapter) {
-		this.categoryPersistenceAdapter = categoryPersistenceAdapter;
-		this.categories = categoryPersistenceAdapter.getAll();
+	final private CustomSet<Category> categories;
+
+	public CategoryRepository(PersistenceAdapter<Category> categoryPersistenceAdapter) {
+		this.categories = new CustomSetPersistenceDecorator<Category>(categoryPersistenceAdapter);
 	}
 
 	public Optional<Category> getByName(CategoryName name) {
@@ -25,16 +27,18 @@ public class CategoryRepository {
 	}
 
 	public Set<Category> getAll(){
-		return categories;
+		return categories.getSet();
 	}
 
 	public void add(Category category) {
 		checkDuplicates(category);
-
 		categories.add(category);
-		categoryPersistenceAdapter.add(category);
 	}
 
+	/**
+	 * Check for duplicates with the domain rules
+	 * @param category
+	 */
 	private void checkDuplicates(Category category) {
 		if (this.getByName(category.getName()).isPresent()) {
 			throw new CategoryAlreadyExists("A category with the name " + category.getName() + " already exits.");
diff --git a/3-Domain/src/main/java/exeptions/ElementAlreadyInSet.java b/3-Domain/src/main/java/exeptions/ElementAlreadyInSet.java
new file mode 100644
index 0000000..894dcc9
--- /dev/null
+++ b/3-Domain/src/main/java/exeptions/ElementAlreadyInSet.java
@@ -0,0 +1,8 @@
+package exeptions;
+
+public class ElementAlreadyInSet extends RuntimeException {
+
+	public ElementAlreadyInSet(String message) {
+		super(message);
+	}
+}
diff --git a/3-Domain/src/main/java/exeptions/ElementNotInSet.java b/3-Domain/src/main/java/exeptions/ElementNotInSet.java
new file mode 100644
index 0000000..19faf2a
--- /dev/null
+++ b/3-Domain/src/main/java/exeptions/ElementNotInSet.java
@@ -0,0 +1,8 @@
+package exeptions;
+
+public class ElementNotInSet extends RuntimeException {
+
+	public ElementNotInSet(String message) {
+		super(message);
+	}
+}
diff --git a/3-Domain/src/main/java/exeptions/LinkAlreadyExists.java b/3-Domain/src/main/java/exeptions/LinkAlreadyExists.java
new file mode 100644
index 0000000..d6e70a8
--- /dev/null
+++ b/3-Domain/src/main/java/exeptions/LinkAlreadyExists.java
@@ -0,0 +1,8 @@
+package exeptions;
+
+public class LinkAlreadyExists extends RuntimeException {
+
+	public LinkAlreadyExists(String message) {
+		super(message);
+	}
+}
diff --git a/3-Domain/src/main/java/exeptions/LinkDoesNotExist.java b/3-Domain/src/main/java/exeptions/LinkDoesNotExist.java
new file mode 100644
index 0000000..105b806
--- /dev/null
+++ b/3-Domain/src/main/java/exeptions/LinkDoesNotExist.java
@@ -0,0 +1,8 @@
+package exeptions;
+
+public class LinkDoesNotExist extends RuntimeException {
+
+	public LinkDoesNotExist(String message) {
+		super(message);
+	}
+}
diff --git a/3-Domain/src/main/java/link/LinkRepository.java b/3-Domain/src/main/java/link/LinkRepository.java
index 57b7a1a..298e39e 100644
--- a/3-Domain/src/main/java/link/LinkRepository.java
+++ b/3-Domain/src/main/java/link/LinkRepository.java
@@ -1,18 +1,19 @@
 package link;
 
+import abstraction.CustomSet;
+import abstraction.CustomSetPersistenceDecorator;
+import abstraction.PersistenceAdapter;
 import exeptions.LinkAlreadyExists;
+import exeptions.LinkDoesNotExist;
 
 import java.util.Optional;
-import java.util.Set;
 
 public class LinkRepository {
 
-	final private LinkPersistenceAdapter linkPersistenceAdapter;
-	final private Set<Link> links;
+	final private CustomSet<Link> links;
 
-	public LinkRepository(LinkPersistenceAdapter linkPersistenceAdapter) {
-		this.linkPersistenceAdapter = linkPersistenceAdapter;
-		this.links = linkPersistenceAdapter.getAll();
+	public LinkRepository(PersistenceAdapter<Link> linkPersistenceAdapter) {
+		this.links = new CustomSetPersistenceDecorator(linkPersistenceAdapter);
 	}
 
 	public Optional<Link> getById(LinkId id) {
@@ -23,10 +24,25 @@ public class LinkRepository {
 		return links.stream().filter(link -> link.getUrl().equals(url)).findFirst();
 	}
 
+	public void removeById(LinkId id) {
+		getById(id).ifPresentOrElse(this::remove, () -> {
+			throw new LinkDoesNotExist("Tried removing a link with id " + id + " but it does not exist.");
+		});
+	}
+
+	public void removeByUrl(LinkUrl url) {
+		getByUrl(url).ifPresentOrElse(this::remove, () -> {
+			throw new LinkDoesNotExist("Tried removing a link with url " + url + " but it does not exist.");
+		});
+	}
+
 	public void add(Link link) {
 		checkDuplicates(link);
+		links.add(link);
+	}
 
-
+	private void remove(Link link) {
+		links.remove(link);
 	}
 
 	private void checkDuplicates(Link newLink) {