A pen name, nom e plume, or literary double, is a pseudonym adopted by an author or their publishers to conceal their identity. A pen name may be used if a writer's real name is likely to be confused with the name of another writer or notable individual, or if their real name is deemed to be unsuitable. Authors who write in fiction and non-fiction, or in different genres, may use pen names to avoid confusing their readers, as in the case of mathematician Charles Dodgson, who wrote fantasy novels under the pen name Lewis Carroll. Some female authors use male pen names, particularly in the 19th century, when writing was a male-dominated profession. A pseudonym may also be used to hide the identity of the author, as in the case of exposé books about espionage or crime, or explicit erotic fiction.