http://www.andreaangella.com/2017/08/practical-c-implementing-equality/
origin - http://www.pipiscrew.com/?p=9673 practical-c-selectmany-in-linq
http://www.andreaangella.com/2017/08/practical-c-implementing-equality/
origin - http://www.pipiscrew.com/?p=9673 practical-c-selectmany-in-linq