Question: Which president of William Eustus also married to Dolley Madison ?
SPARQL:
 SELECT DISTINCT ?uri WHERE { <http://dbpedia.org/resource/Dolley_Madison> <http://dbpedia.org/ontology/spouse> ?uri. <http://dbpedia.org/resource/William_Eustis> <http://dbpedia.org/property/president> ?uri}