gistfile1.cs

  private void removeButton_Click(object sender, EventArgs e)
        {
            if (removeIsbnRadioButton.Checked)
            {
                    foreach (Book book in books)
                    {
                        if (book.Isbn.Normalize().Equals(searchBookTextBox.Text.Normalize()))
                        {
                            books.Remove(book);
                            break;
                        }
                    }
            }

            if (removeLastNameRadioButton.Checked)
            {
                foreach (Book book in books)
                {
                    if (book.LastName == removeTextBox.Text)
                    {
                        books.Remove(book);
                        break;
                    }
                }

            }

            if (removeTitleRadioButton.Checked)
            {
                foreach (Book book in books)
                {
                    if (book.Title == removeTextBox.Text)
                    {
                        books.Remove(book);
                    }
                }
            }
        }