What is {population} of {City of London} that is {point in time} is {1971-0-0} ?
In London, 1971, what was the population?
What was the population of London in 1971?
SELECT ?d WHERE { resource:City_of_London property:population ?z . ?z property:population ?d . FILTER ( CONTAINS ( YEAR ( ?a ) , '1971' ) ) . ?z property:point_in_time ?a }
select distinct ?obj  where {
?statement <http://www.w3.org/1999/02/22-rdf-syntax-ns#subject> <http://wikidata.dbpedia.org/resource/Q23311> .
?statement <http://www.w3.org/1999/02/22-rdf-syntax-ns#predicate> <http://www.wikidata.org/entity/P1082> .
?statement <http://www.w3.org/1999/02/22-rdf-syntax-ns#object> ?obj .
?statement <http://www.wikidata.org/entity/P585> <1971-0-0>
} 

SELECT ?obj WHERE { wd:Q23311 p:P1082 ?s . ?s ps:P1082 ?obj . ?s pq:P585 ?x filter(contains(YEAR(?x),'1971')) }