How to ignore build in functions and class name when we are comparing coding files?

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C#

how to hide build in library functions, identifier or such stuffs of code when we are comparing two code files and we want to ignore these things which are common ??????

is there any build in function to use in .NET IDE any idea about it...............

like here

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.Security.Cryptography;


class file1
  {
     public void add()
  {
    int a;
    int b;

    int c = a + b;

    console.WriteLine("print the sum" + c);
   }
  }

and here second

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.Security.Cryptography;

class file2
  {
     public void multiply()
  {
    int a;
    int b;

    int c = a * b;

    console.WriteLine("print the sum" + c);
   }
  }

now if i want to compare these two input coding files so i want to ignores its build_in functions or keywords ect so would we do this .......


i just gave the example of these files i am working on comparing files for their similarities to check they are copied or not and now i faced this problem that i have to ignore such all build in functions otherwise it would give wrong answer for their similarities...