anchor.diff:      ;
   
   set
  -    : SET SPACE+ assign (',' assign)*
  +    : (SET1 | SET2) SPACE+ assign (',' assign)*
       ;
   
   assign
  
positive.code:     : R E A D
      ;
  
  SET
      : S E T
      ;
  
  TCOMMIT
  
negative.code:     : FOR SPACE+ term EQUALS term COLON term SPACE* (command SPACE?)* COLON (term (LT | GT) term)
      ;
  
  write
      : (WRITE1 | WRITE2) SPACE* arglist
      ;
  
  quit
      : QUIT
      ;
  
  BREAK
      : B R E A K
      ;
  