name the common serving line of saarbrücken-ost station and saarbrücken hauptbahnhof ?
SELECT DISTINCT var_uri where brack_open dbr_Saarbrücken-Ost_station dbo_servingRailwayLine var_uri sep_dot dbr_Saarbrücken_Hauptbahnhof dbo_servingRailwayLine var_uri brack_close