SELECT DISTINCT ?uri WHERE { ?x <http://dbpedia.org/ontology/opponent> <http://dbpedia.org/resource/John_Hospers> . ?x <http://dbpedia.org/ontology/incumbent> ?uri . }
Who was the president during the time the opponent of John Hospers was in the office?
SELECT DISTINCT ?a WHERE { ?t property:incumbent ?a . . ?t property:opponent resource:John_Hospers }
Richard Nixon
The incumbent of the politician whose opponent is John Hospers is [Richard Nixon].
The president of a politician whose opponent is John McCain [Richard Nixon].
The incumbent of the politician whose opponent is him is [Richard Nixon].
[Richard Nixon] was the president at the time the opponent of him.