These commands define (or redefine) a command.
- cmd A command name beginning with a \. For \newcommand it must
not be already defined and must not begin with \end; for
\renewcommand it must already be defined.
- args An integer from 1 to 9 denoting the number of arguments of
the command being defined. The default is for the command to
have no arguments.
- def The text to be substituted for every occurrence of cmd; a
parameter of the form #n in cmd is replaced by the text of the
nth argument when this substitution takes place.