public override string ToString()
 {
     return($"{GetPeopleString(Authors.ToList<IPerson>())} ({PublicationDateTime.ToFormattedString()}). {Name}. {Publisher.ToString()}");
 }
 public string ToShortString()
 {
     return($"({GetShortPeopleString(Authors.ToList<IPerson>())}, {PublicationDateTime.ToFormattedString()})");
 }