C# How to derives A from B, where B in different .cs file

I have question about inheritance of c# in Unity 3D.

Let's say, below is my first file, parent.cs :

 using System;
 
 public abstract class parent {
     private string _name;
 
     public parent() {
         _name = "my name is ";
     }
     
     public void appendName(string _appendThis) {
         _name += _appendThis;
     }
     
     public string getName() {
         return _name;
     }
 }

Then, below is my second file, child.cs :

 using UnityEngine;
 using System;
 
 public class child : parent {
     public child() {
         base.appendName("gsunity");
     }
 
     public string SayName() {
         return base.getName();
     }
 }

Then I have last file, myunity.cs :

 using UnityEngine;
 using System;
 
 public class myunity : MonoBehaviour {
     private child guy = new child();
 
     void Start() {
         Debug.Log(guy.SayName());
     }
 }

My Question is, how to using another cs file in Unity 3D, like three c# script above as the example?

---

Edited in July 21, 2011.

There was a lot of wrong statement in my script before. So I alter all above script after I finish downloading Unity and tried it.

The parent class must declared like this: public abstract class parent I was forgot to write public keyword before the abstract keyword.

Now my script can work as it should. I just had to Drag and Drop the myunity.cs to an object that I created before. And the other script (parent.cs and child.cs) was run automatically.

My problem now has been solved. Thank's all