public static IEnumerable <MessageAbstraction> AttachMessage(this IEnumerable <MessageAbstraction> messages,
                                                              MessageAbstraction otherMessage)
 => messages.Append(otherMessage);
 public static IEnumerable <MessageAbstraction> AttachMessage(this MessageAbstraction message,
                                                              MessageAbstraction otherMessage) => new[] { message, otherMessage };
 public static IEnumerable <MessageAbstraction> AttachMessages(this MessageAbstraction message,
                                                               IEnumerable <MessageAbstraction> otherMessages)
 => new[] { message }.AttachMessages(otherMessages);