\newcommand
 \newcommand{cmd}[args]{def}
 \renewcommand{cmd}[args]{def}
 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.