protected function _createCompareExpression( $op, array $pair )
	{
		if( ( list( $name, $value ) = each( $pair ) ) === false ) {
			throw new MW_Common_Exception( sprintf( 'Invalid compare condition array "%1$s"', json_encode( $pair ) ) );
		}

		return $this->compare( $op, $name, $value );
	}