You could use a query like this one to find authors of more than one method:
PREFIX rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#>
PREFIX owl: <http://www.w3.org/2002/07/owl#>
PREFIX xsd: <http://www.w3.org/2001/XMLSchema#>
PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#>
PREFIX : <http://www.semanticweb.org/vyacheslav/ontologies/2013/11/untitled-ontology-6#>
SELECT ?author (count(?method) as ?numMethods)
WHERE {
?method :hasAuthor ?author .
?author a :Author .
}
group by ?author
having (?numMethods > 1)
The results look like this:

A couple of notes though. Ideally you'd want to specify that the method is a actually a method. First, it's generally a good idea to name your classes with singular forms of the word, since it's more natural to say that an individual method “is a Method” rather than “is a Methods”. Anyhow, since the class is named Methods, it would be nice to write the query body as
?method a :Methods .
?method :hasAuthor ?author .
?author a :Author .
but this won't work unless you have a reasoner attached (so that individuals that are declared as members of subclasses of Methods can also be inferred to be members of Methods).