Head notes of court decisions require skill and thought to summarize the key principles of law and facts in concise language. As such, they are entitled to copyright protection as original literary works. While historical works themselves are not copyrightable, any new knowledge extracted from them can be copyrighted. Titles of books and cartoons generally cannot be copyrighted, but can be protected by laws around passing off. Copyright subsists in letters as original works, with the author holding copyright over private letters and employers holding copyright over commercial or government letters written by employees.