what is the opera genre of an opera whose first performance occurred before 2013-09-20?
Entity Entity Entity Entity Entity Entity Entity Entity Entity Entity Entity Entity Entity Entity Entity Entity Entity Entity Entity Entity Entity Entity Entity Entity
m.02vqkqk m.01_22_ m.04dg7h2 m.04b7znm m.04b2fpl m.04m282 m.04mkyt5 m.02g129 m.052pc27 m.04b7d2r m.052jxz1 m.03c8g9x m.04dg603 m.0gd6k3 m.0d8gp m.04llstk m.052bg4 m.04b7q58 m.0332nd m.0g65wk m.04d7t6w m.04hynqs m.04dg7k6 m.0gghh3
Romantische Oper Opera seria Opera in three acts Opera in one act Opera in two acts Opéra comique Opera in five acts Singspiel Fairy tale opera Children's opera Opera in four acts Literaturoper Musical action Rescue opera Opera buffa Legende dramatique Lyric tragedy Comic opera in two acts Comic opera Chamber opera Quasi un melodramma in three acts Lyric comedy Marionette opera Opera semi-seria
class class literal
opera.opera_genre opera.opera 2013-09-20^^http://www.w3.org/2001/XMLSchema#date
opera.opera_genre opera.opera type.datetime
Opera Genre Opera 2013-09-20
none none <
opera.opera.genre music.composition.date_of_first_performance
Genre Date of first performance
PREFIX rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#> PREFIX : <http://rdf.freebase.com/ns/> 
SELECT (?x0 AS ?value) WHERE {
SELECT DISTINCT ?x0  WHERE { 
?x0 :type.object.type :opera.opera_genre . 
?x1 :type.object.type :opera.opera . 
FILTER (?x2 < "2013-09-20-08:00"^^<http://www.w3.org/2001/XMLSchema#date>)
?x1 :opera.opera.genre ?x0 . 
?x1 :music.composition.date_of_first_performance ?x2 . 
FILTER ( ?x0 != ?x1 && ?x0 != ?x2 && ?x1 != ?x2  )
}
}
(AND opera.opera_genre (JOIN (R opera.opera.genre) (lt music.composition.date_of_first_performance 2013-09-20^^http://www.w3.org/2001/XMLSchema#date)))