anchor.diff:     : STRING
      ;
   
  -verb
  +verbname
      : STRING
      ;
   
  
positive.code:    ;
  
  command
     : prop ':' function
     ;
  
  function
     : verb ('(' expressionlist ')')?
     ;
  
  prop
  
negative.code:    ;
  
  programdecl
     : '@program' programname ':' verbname
     ;
  
  statement
  