Count the different affiliations of the authors of 'On computing the inverse DFT'.
How many different affiliations do the authors of 'On computing the inverse DFT' have?
SELECT (COUNT(DISTINCT ?answer) AS ?count) WHERE { <https://dblp.org/rec/journals/tsp/DuhamelPE88> <https://dblp.org/rdf/schema#authoredBy> ?x . ?x <https://dblp.org/rdf/schema#primaryAffiliation> ?answer }
<https://dblp.org/rec/journals/tsp/DuhamelPE88>