query: #songs named after a day of the week
  SELECT ?day ?dayLabel ?item ?itemLabel ?performer ?performerLabel WHERE {
    ?day wdt:P31 wd:Q41825.
    ?item wdt:P31/wdt:P279* wd:Q7366; wdt:P138 ?day.
    OPTIONAL{?item wdt:P175 ?performer}
    SERVICE wikibase:label { bd:serviceParam wikibase:language "[AUTO_LANGUAGE],en". }
  }
  ORDER BY ?day