Add Lesson 4 Task 4

Lesson_4/Task_4/Interfaces/IFlyable.cs

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+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace LiskovSubstitution.Interfaces
+{
+    public interface IFlyable
+    {
+        public void Fly();
+    }
+}

Lesson_4/Task_4/Perfomance.cs

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+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace LiskovSubstitution
+{
+    public class Perfomance
+    {
+        public void PerformActions()
+        {
+            //Hmmmm...
+        }
+    }
+}

Lesson_4/Task_4/Program.cs

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+using LiskovSubstitution.Vehicles;
+
+// A plane has an engine, and is able to fly
+Plane plane = new Plane();
+plane.Fly();
+plane.StartEngine();
+
+// A car cannot fly, CS1061 if attempted
+Car car = new Car();
+// car.Fly();
+car.StartEngine();
+
+// Same for motorcycle
+Motorcycle motorcycle = new Motorcycle();
+// motorcycle.Fly();
+motorcycle.StartEngine();

Lesson_4/Task_4/Task_4.csproj

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+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>net7.0</TargetFramework>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+  </PropertyGroup>
+
+</Project>

Lesson_4/Task_4/Vehicles/Car.cs

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+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace LiskovSubstitution.Vehicles
+{
+    public class Car : Vehicle
+    {
+    }
+}

Lesson_4/Task_4/Vehicles/Motorcycle.cs

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+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace LiskovSubstitution.Vehicles
+{
+    public class Motorcycle : Vehicle
+    {
+    }
+}

Lesson_4/Task_4/Vehicles/Plane.cs

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+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+using LiskovSubstitution.Interfaces;
+
+namespace LiskovSubstitution.Vehicles
+{
+    public class Plane : Vehicle, IFlyable
+    {
+        public virtual void Fly()
+        {
+            Console.WriteLine("It's flying?");
+        }
+    }
+}

Lesson_4/Task_4/Vehicles/Vehicle.cs

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+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace LiskovSubstitution.Vehicles
+{
+    public class Vehicle
+    {
+        public virtual void StartEngine()
+        {
+            Console.WriteLine("The engine is starting");
+        }
+    }
+}