anchor.diff:  * command word and its post-conditional, if present, and the argument.
   */
   break_
  -   : (BREAK) postcondition?
  +   : BREAK postcondition?
      ;
   
   do_
  -   : (DO) postcondition? SPACE + identifier (LPAREN paramlist? RPAREN)?
  +   : DO postcondition? SPACE + identifier (LPAREN paramlist? RPAREN)?
      ;
   
   for_
  
positive.code:    ;
  
  write_
     : (WRITE) postcondition? SPACE + arglist
     ;
  
  xecute_
  
negative.code:    ;
  
  new_
     : NEW postcondition? SPACE + arglist
     ;
  
  quit_
     : QUIT postcondition? (SPACE + term)?
     ;
  
  read_
     : READ postcondition? SPACE + arglist
     ;
  
  set_
     : SET postcondition? SPACE + assign (',' assign)*
     ;
  
  view_
  