public Student(string name, Genre prefGenre, Library lib)
        {
            if (name == null || lib == null)
            {
                throw new ArgumentNullException();
            }
            else
            {
                _name = name;
                _preferedGenre = prefGenre;

                lib.CollectionChanged += LibChanged;
            }
        }
        static void Main(string[] args)
        {
            var lib = new Library();

            Student studentf = new Student("Vasya", Genre.Fantastic, lib);
            Student studentc = new Student("Petya", Genre.Computer, lib);

            lib.AddBook(new Book("CLR via C#", "Jeffrey Richter", Genre.Computer));
            lib.AddBook(new Book("C# in a nutshell", "Joseph Albahari", Genre.Computer));
            lib.AddBook(new Book("Win10", "Andy Rathbone", Genre.Computer));
            lib.AddBook(new Book("The Time Machine", "H. G. Wells", Genre.Fantastic));
            lib.AddBook(new Book("The Lord of the Rings", "J. R. R. Tolkien", Genre.Fantastic));

            lib.GetBook("C# in a nutshell");

            Console.ReadKey();
        }