cor-ten steel is the child material class of what material?
Entity
m.08g_fq
Weathering steel
class entity
engineering.material m.03q7pqt
engineering.material engineering.material
Material Cor-ten steel
none none
engineering.material.subclass
Child material class
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 :engineering.material . 
VALUES ?x1 { :m.03q7pqt } 
?x0 :engineering.material.subclass ?x1 . 
FILTER ( ?x0 != ?x1  )
}
}
(AND engineering.material (JOIN engineering.material.subclass m.03q7pqt))