When did Ludwig Wittgenstein graduate as a Doctor of Philosophy?
SELECT ?value1 ?value2 WHERE { wd:Q9391 p:P512 ?s . ?s ps:P512 wd:Q752297 . ?s pq:P585 ?value1 . ?s pq:P69 ?value2 }
ludwig wittgenstein: Q9391 doctor of philosophy: Q752297