anchor.diff:  insert	:		'insert into' tid '(' fid ')' 'values' '(' vid ')' 'where' pred
   				;
   
  +update	:		'update' tid 'set' assi 'where' pred
  +				;
  +
   fid			:		ID (',' ID)*
   				;
   
  
positive.code: 			
  stat		:		select EOS
  				|		insert EOS
  				|		EOS
  				;
  
  
negative.code: 				;
  
  vid			:		expr (',' expr)*
  				;
  
  assi		:		assi (',' assi)*
  				|		ID '=' expr
  				|		assi
  				;
  
  pred		:		pred ('and'|'or') pred
  