SELECT DISTINCT ?uri WHERE { ?x <http://dbpedia.org/ontology/opponent> <http://dbpedia.org/resource/Benjamin_Spock> . ?x <http://dbpedia.org/property/incumbent> ?uri . }
Who was the president at the time when the opponent of Benjamin Spock held office?
SELECT DISTINCT ?l WHERE { ?l property:opponent resource:Benjamin_Spock . ?l property:incumbent ?l . }
Richard Nixon
The incumbent president of the people whose opponent is Benjamin Spock is [Richard Nixon].
A recalcitrant president of a people whose opponent is Benjamin Spock [Richard Nixon].
The incumbent president of the people whose opponent is the person is [Richard Nixon].
[Richard Nixon] was the president at that time.