which comet is associated with an astronomical observatory with observatory pcas?
Entity Entity
m.02sdh9 m.0f0fm
4015 Wilson–Harrington 2060 Chiron
class class entity
astronomy.comet astronomy.astronomical_observatory m.03zr1p
astronomy.comet astronomy.astronomical_observatory astronomy.astronomical_survey_project_organization
Comet Astronomical Observatory pcas
none none none
astronomy.astronomical_observatory.discoveries astronomy.astronomical_survey_project_organization.observatory
Discoveries Observatory
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 :astronomy.comet . 
?x1 :type.object.type :astronomy.astronomical_observatory . 
VALUES ?x2 { :m.03zr1p } 
?x1 :astronomy.astronomical_observatory.discoveries ?x0 . 
?x2 :astronomy.astronomical_survey_project_organization.observatory ?x1 . 
FILTER ( ?x0 != ?x1 && ?x0 != ?x2 && ?x1 != ?x2  )
}
}
(AND astronomy.comet (JOIN (R astronomy.astronomical_observatory.discoveries) (JOIN (R astronomy.astronomical_survey_project_organization.observatory) m.03zr1p)))