using System;
using System.Collections.Generic;
                    
public class Program
{
    public static void Main()
    {
        // we have 3 items: A, B and C
        var a = new Item {Name = "A"};
        var b = new Item {Name = "B"};
        var c = new Item {Name = "C"};
        
        var items = new List<Item>()
        {
            a,
            b,
            c,
        };
        
        // add B as an alternative to A
        a.Alternatives.Add(b);
        
        // that means A is an alternative to B
        b.Alternatives.Add(a);
        
        // add C as an alternative to B
        b.Alternatives.Add(c);
        
        // that means B is an alternative to C
        c.Alternatives.Add(b);
        
        // and now the complication: it means that C is an alternative to A too, because A is alternative to B
        a.Alternatives.Add(c);
        
        // and it means A is an alternative to C too
        c.Alternatives.Add(a);

        // let's print the alternatives
        foreach(var item in items)
        {
            Console.Write($"Item {item.Name} has the alternatives: ");
            
            foreach(var alternative in item.Alternatives)
            {
                Console.Write($"{alternative.Name} ");
            }
            
            Console.WriteLine();
        }
        
        // Result:
        // Item A has the alternatives: B C 
        // Item B has the alternatives: A C 
        // Item C has the alternatives: B A 

        // then... trying to add/remove numerous alternatives... 
        // would make all thing way to complicated to sync all item.Alternatives in each
    }
}

public class Item 
{
  public string Name {get; set;}
  public List<Item> Alternatives {get; set;} = new();
}

using System;
using System.Collections.Generic;
                    
public class Program
{
    public static void Main()
    {
        // we have 3 items: A, B and C
        var a = new Item {Name = "A"};
        var b = new Item {Name = "B"};
        var c = new Item {Name = "C"};
        
        var items = new List<Item>()
        {
            a,
            b,
            c,
        };
        
        // add B as an alternative to A
        a.Alternatives.Add(b);
        
        // that means A is an alternative to B
        b.Alternatives.Add(a);
        
        // add C as an alternative to B
        b.Alternatives.Add(c);
        
        // that means B is an alternative to C
        c.Alternatives.Add(b);
        
        // and now the complication: it means that C is an alternative to A too, because A is alternative to B
        a.Alternatives.Add(c);
        
        // and it means A is an alternative to C too
        c.Alternatives.Add(a);

        // let's print the alternatives
        foreach(var item in items)
        {
            Console.Write($"Item {item.Name} has the alternatives: ");
            
            foreach(var alternative in item.Alternatives)
            {
                Console.Write($"{alternative.Name} ");
            }
            
            Console.WriteLine();
        }
        
        // Result:
        // Item A has the alternatives: B C 
        // Item B has the alternatives: A C 
        // Item C has the alternatives: B A 

        // then... trying to add/remove numerous alternatives... 
        // would make all thing way to complicated to sync all item.Alternatives in each
    }
}

public class Item 
{
  public string Name {get; set;}
  public List<Item> Alternatives {get; set;} = new();
}