which subsidiary of maersk air serves both cologne bonn airport and cologne bonn airport ?
select distinct var_uri where brack_open dbr_Maersk_Air dbo_subsidiary var_uri sep_dot var_uri dbo_targetAirport dbr_Cologne_Bonn_Airport sep_dot var_uri dbo_targetAirport dbr_Cologne_Bonn_Airport sep_dot brack_close