query: #Number of public library organisations in Dutch provinces
  SELECT 
  ?province ?provinceLabel ?item ?itemLabel 
  #(COUNT(?municipality) AS ?AantalOBVestigingen)  
  #(GROUP_CONCAT(DISTINCT ?itemLabel ; separator = " --- ") as ?OBVestigingen)
  
  WHERE { #?itemLabel
    ?item wdt:P31 wd:Q28564. #public library
    ?item wdt:P31 wd:Q28324850. #library system 
    ?item wdt:P17 wd:Q55. #from the Netherlands
    ?item wdt:P159 ?headquarters. #headquarter location
    ?headquarters wdt:P131 ?municipality.
    ?municipality wdt:P131 ?province.
    #FILTER( ?instanceOf IN(wd:Q2039348)). #filter only the value "municipality of the Netherlands" Q2039348
    SERVICE wikibase:label { bd:serviceParam wikibase:language "nl" .
                           }
  }
  #GROUP BY ?municipality ?municipalityLabel