How many {participant of} are for {Steffi Graf} ?
Steffi Graf has how many participants to play with?
How many participants are playing with Steffi Graf?
SELECT ( COUNT ( ?c ) AS ?b ) { resource:Steffi_Graf property:participant_in ?c }
SELECT (COUNT(?obj) AS ?objs ) {
?statement <http://www.w3.org/1999/02/22-rdf-syntax-ns#subject> <http://wikidata.dbpedia.org/resource/Q11662> .
?statement <http://www.w3.org/1999/02/22-rdf-syntax-ns#predicate> <http://www.wikidata.org/entity/P1344> .
?statement <http://www.w3.org/1999/02/22-rdf-syntax-ns#object> ?obj .
} 

SELECT (COUNT(?obj) AS ?value ) { wd:Q11662 wdt:P1344 ?obj }
5