Find the number of authors of the paper 'Designing and building powerful, inexpensive robots for evolutionary research'.
How many authors does 'Designing and building powerful, inexpensive robots for evolutionary research' have?
SELECT ?answer WHERE { <https://dblp.org/rec/conf/gecco/Soule13> <https://dblp.org/rdf/schema#numberOfCreators> ?answer }
<https://dblp.org/rec/conf/gecco/Soule13>