anchor.diff:  //                VAR EQUAL aggregate_atom;
   
   //关系运算表达式
  -relation_expr : ((MINUS)? term) relation_op ((MINUS)? term);
  +//relation_expr : ((MINUS)? term) relation_op ((MINUS)? term);
  +comparison_literal : ((MINUS)? term) relation_op ((MINUS)? term);
   
   
   //规则头部
  
positive.code: //数字
  bit_number : unary_op? natural_number;
  //关系运算符(comparison predicates)
  relation_op : LESS_THAN | LEQ | GREATER_THAN | GEQ | EQUAL | DOUBLE_EQUAL | NEQ;
  
  //简单四则运算算术表达式，不加括号
  simple_arithmetic_expr :
  
negative.code:     CONSTANT LPAREN term (COMMA term)* RPAREN;
  
  //文字
  literal : atom | MINUS atom | NAF_NOT literal | comparison_literal;
  
  //缺省文字
  //default_literal : NAF_NOT literal;
  