Archaic command, use PEDIT instead.
DEF tells VISTA to begin a procedure definition. It is mostly historical, as procedures can now be defined using a real editor with the PEDIT command. The command DEF will prompt you with a series of line numbers, beginning with the number specified in the command line. If no number was given, the first command will be on line 1. You are to specify a command for each line. Type the command you want on that line, then hit RETURN. VISTA will check the command for proper syntax, and store it in the procedure buffer. Then VISTA will prompt you with the number of the next line. Continue typing in commands until the entire procedure has been entered. To tell VISTA that you have entered the entire procedure, type END or SAME (q.v.). A maximum length of 2500 lines is allowed in a procedure, and each line is allowed a maximum length of 80 characters.