Between 'Didaktische Aspekte der Dialogformen bei Auskunftlehrsystemen' and 'Third-generation wireless services for homeland security', which paper was published earlier?
Which one was published first, 'Didaktische Aspekte der Dialogformen bei Auskunftlehrsystemen' or 'Third-generation wireless services for homeland security'?
SELECT DISTINCT ?answer WHERE { <https://dblp.org/rec/conf/rgu/MartinH74> <https://dblp.org/rdf/schema#yearOfPublication> ?x . <https://dblp.org/rec/journals/bell/BalachandranBDK04> <https://dblp.org/rdf/schema#yearOfPublication> ?y . BIND(IF(?x < ?y, <https://dblp.org/rec/conf/rgu/MartinH74>, <https://dblp.org/rec/journals/bell/BalachandranBDK04>) AS ?answer) }
<https://dblp.org/rec/conf/rgu/MartinH74> <https://dblp.org/rec/journals/bell/BalachandranBDK04>