static void Main(string[] args)
{
Console.WriteLine("### Observer Pattern ###");
// Create Opportunity and attach competitors
Opportunity opp = new Opportunity("Active", 120.00);
opp.Attach(new Competitor("JLL"));
opp.Attach(new Competitor("Nordstrom"));
// Fluctuating prices will notify investors
opp.Price = 120.10;
opp.Price = 121.00;
opp.Price = 120.50;
opp.Price = 120.75;
// Wait for user
Console.ReadKey();
}