Argument: None
Key sequence: None
Without a prefix argument, this undefines the current top level definition. That is, the defining form around or preceding the current point.
With a non-nil prefix argument, this does not undefine the definition but instead inserts into the buffer a Lisp form which, if evaluated, would undefine the definition.
Argument: None
Key sequence: None
Prompts for the name of an Editor command, and undefines that command.