anchor.diff:  LIKE : 'like' ;
   LIMIT : 'limit' ;
   LOCK	:	'lock';
  +MERGE : 'merge' ;
   NOT : 'not' ;
   NOTFOUND:	'notfound';
   NULL : 'null' ;
  
positive.code:     | delete_statement
      | insert_statement
      | lock_table_statement
      | rollback_statement
      | savepoint_statement
      | select_statement
  
negative.code: 
  lock_table_statement :
          LOCK TABLE swallow_to_semi
      ;
  
  merge_statement :
          MERGE swallow_to_semi?
      ;
  
  rollback_statement :
  