Question about generics constraining Types

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace Genericclasses
{
    class Program
    {
        static void Main(string[] args)
        {
            somegeneric<forbidden> b = new somegeneric<forbidden>();
            somegeneric<forbidden> c = new somegeneric<forbidden>();
            b.a.value = 10;
            Console.ReadLine();
        }
    }
    class forbidden
    {
        public int value;
       

    }
    class somegeneric<T> where T:forbidden
    {
        public T a;
      
    }
    class somegeneric2<T> : somegeneric<T> where T:forbidden
    {
    }
   
}