diff --git a/lesson#24 - Observer Design Pattern/ObserverDesignPattern/main.d b/lesson#24 - Observer Design Pattern/ObserverDesignPattern/main.d
deleted file mode 100644
index 1d34cce..0000000
--- a/lesson#24 - Observer Design Pattern/ObserverDesignPattern/main.d	
+++ /dev/null
@@ -1,67 +0,0 @@
-import std.stdio: writeln;
-
-interface IObserver {
-	void update(string msg);
-}
-
-class WhatsApp {
-	private IObserver[] list;
-
-	this() {}
-	~this() {}
-
-	void addClient(IObserver o) {
-		list ~= o;
-	}
-
-	void removeClient(IObserver o) {
-		import std.algorithm: remove;
-		list = list.remove!(a => a is o);
-	}
-
-	void notify(string msg) {
-		foreach(client; list) {
-			client.update(msg);
-		}
-	}
-}
-
-class Person: IObserver {
-	string name;
-
-	this(string name) {
-		this.name = name;
-	}
-
-	void update(string msg) {
-		writeln(name, "\t: notified. [", msg, "]");
-	}
-}
-
-void main() {
-	WhatsApp app = new WhatsApp();
-
-	Person anna = new Person("Anna");
-	Person john = new Person("John");
-	Person markus = new Person("Markus");
-
-	app.addClient(anna);
-	app.addClient(john);
-	app.addClient(markus);
-
-	app.notify("hello, world!");
-
-	app.removeClient(john);
-
-	app.notify("john left the conversation");
-}
-
-
-
-
-
-
-
-
-
-
diff --git a/lesson#24 - Observer Design Pattern/main.d b/lesson#24 - Observer Design Pattern/main.d
new file mode 100644
index 0000000..53d063f
--- /dev/null
+++ b/lesson#24 - Observer Design Pattern/main.d	
@@ -0,0 +1,65 @@
+import std.stdio: writeln;
+
+// IObserver interface
+interface IObserver {
+    void update(string msg);
+}
+// Person (observer)
+class Person: IObserver {
+    string name;
+
+    this(string name) {
+	this.name = name;
+    }
+
+    void update(string msg) {
+	writeln(name, "\t: notified. [", msg, "]");
+    }
+}
+
+// WhatsApp (subject)
+class WhatsApp {
+    private IObserver[] list;
+
+    this() {}
+    ~this() {}
+
+    void addClient(IObserver o) {
+	list ~= o;
+    }
+
+    void removeClient(IObserver o) {
+	import std.algorithm: remove;
+	list = list.remove!(a => a is o);
+    }
+
+    void notify(string msg) {
+	foreach(client; list) {
+	    client.update(msg);
+	}
+    }
+}
+
+void main() {
+    WhatsApp conversation = new WhatsApp();
+
+    Person anna = new Person("Anna");
+    Person john = new Person("John");
+    Person markus = new Person("Markus");
+    
+    conversation.addClient(anna);
+    conversation.addClient(john);
+    conversation.addClient(markus);
+
+    conversation.notify("hello, world!");
+
+    conversation.removeClient(john);
+    
+    conversation.notify("john left the conversation");
+}
+
+
+
+
+
+
diff --git a/lesson#24 - Observer Design Pattern/slides/observer1280x800.jpg b/lesson#24 - Observer Design Pattern/slides/observer1280x800.jpg
deleted file mode 100644
index 1b6e975..0000000
Binary files a/lesson#24 - Observer Design Pattern/slides/observer1280x800.jpg and /dev/null differ