public GSM(string model, string manufacturer, decimal? price = null, string owner = null, Battery battery = null, Display display = null)
: this(model, manufacturer)
{
this.Price = price;
this.Owner = owner;
this.Battery = battery;
this.Display = display;
}
public GSM(string model, string manufacturer, Display display)
: this(model, manufacturer)
{
this.Display = display;
}