15.20.1  COMMAND 

     DEFINE COMMAND new_command "command string"

This  defines  a  new command as the command string.  New commands must be
different from existing commands, and are only used if an existing command
is  not  found.  There is a limit of 3 command substitutions in a row, and
1000 total substitutions per input line.   The  limit  on  the  number  of
substitutions per line may be modified by SET COMMAND.

                                  example
     DEFINE COMMAND EDT "SPAWN EDT"
Defines the command EDT so you may edit a file while using TOPDRAWER.
     DEFINE COMMAND MAIL "SPAWN MAIL"
Defines  the  command  MAIL  so  you  may use the mail utility while using
TOPDRAWER.
     DEFINE COMMAND @ "SET FILE INPUT="
Defines @ to work similarly to @ in VMS.  @filename will get commands from
the specified file.
     DEFINE  COMMAND  EDAT "LIST DATA FILE=DAT.TMP;EDT DAT.TMP;DELETE ALL;
SET FILE IN=DAT.TMP"
Defines the command EDAT to allow you to edit the current data.