How many {operator} are for {London Underground} ?
The London Underground employs what number of operators?
What's the total amount of operators employed in the London Underground?
SELECT ( COUNT ( ?q ) AS ?s ) { resource:London_Underground property:operator ?q }
SELECT (COUNT(?obj) AS ?objs ) {
?statement <http://www.w3.org/1999/02/22-rdf-syntax-ns#subject> <http://wikidata.dbpedia.org/resource/Q20075> .
?statement <http://www.w3.org/1999/02/22-rdf-syntax-ns#predicate> <http://www.wikidata.org/entity/P137> .
?statement <http://www.w3.org/1999/02/22-rdf-syntax-ns#object> ?obj .
} 

SELECT (COUNT(?obj) AS ?value ) { wd:Q20075 wdt:P137 ?obj }
1