static void Main(string[] args)
{
List<decimal> decs = new List<decimal> { 1, 2, 3, 4, 5, 6, 7, 8, 9 };
BankAccounts first = new BankAccounts();
first.on_add += n => Console.WriteLine("First add {0}",n);
first +=20;
BankAccounts second = new BankAccounts();
second.on_add += n => Console.WriteLine("Second add {0}", n);
second += decs;
first += second;
Console.WriteLine("Sum of first = {0}", first.Sum());
Console.WriteLine("Sum of both = {0}", new BankAccounts().Add(first).Add(second).Sum());
Console.WriteLine("first: {0}", first.ToString());
Console.ReadKey();
}