what is the {start time} for {Bolesław Bierut} has {position held} as {President of Poland} ?
When did Boleslaw Bierut become Poland's President?
When was Boleslaw Bierut came to the position of President of Poland?
SELECT ?v WHERE { ?w property:position_held resource:President_of_the_Republic_of_Poland . ?w property:start_time ?v . resource:Bolesław_Bierut property:position_held ?w }
select distinct ?value  where {
?statement <http://www.w3.org/1999/02/22-rdf-syntax-ns#subject> <http://wikidata.dbpedia.org/resource/Q55832> .
?statement <http://www.w3.org/1999/02/22-rdf-syntax-ns#predicate> <http://www.wikidata.org/entity/P39> .
?statement <http://www.w3.org/1999/02/22-rdf-syntax-ns#object> <http://wikidata.dbpedia.org/resource/Q1054799> .
?statement <http://www.wikidata.org/entity/P580> ?value. 
} 

SELECT ?value WHERE { wd:Q55832 p:P39 ?s . ?s ps:P39 wd:Q1054799 . ?s pq:P580 ?value}