Find the number of authors of the paper 'Usage-Based Pricing and Competition in Congestible Network Service Markets'.
How many authors does the publication 'Usage-Based Pricing and Competition in Congestible Network Service Markets' have?
SELECT ?answer WHERE { <https://dblp.org/rec/journals/ton/Ma16a> <https://dblp.org/rdf/schema#numberOfCreators> ?answer }
<https://dblp.org/rec/journals/ton/Ma16a>