How many {interaction} are to/by {weak interaction} ?
How many interactions are weak?
How many interactions constitute a weak interaction ?
SELECT ( COUNT ( ?m ) AS ?l ) { ?m property:interaction resource:weak_interaction }
SELECT (COUNT(?sub) AS ?subs ) {
?statement <http://www.w3.org/1999/02/22-rdf-syntax-ns#subject> ?sub .
?statement <http://www.w3.org/1999/02/22-rdf-syntax-ns#predicate> <http://www.wikidata.org/entity/P517> .
?statement <http://www.w3.org/1999/02/22-rdf-syntax-ns#object> http://wikidata.dbpedia.org/resource/Q11418 .
} 

SELECT (COUNT(?sub) AS ?value ) { ?sub wdt:P517 wd:Q11418 }
42