what is the {start time} for {Charles Lyell} has {position held} as {President of the Geological Society of London} ?
When was Charles Lyell President of the Geological Society of London?
When did Charles Lyell hold the position of  President of the Geological Society of London?
SELECT ?a WHERE { resource:Charles_Lyell property:position_held ?k . ?k property:position_held resource:President_of_the_Geological_Society_of_London . ?k property:start_time ?a }
select distinct ?value  where {
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?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/Q7241336> .
?statement <http://www.wikidata.org/entity/P580> ?value. 
} 

SELECT ?value WHERE { wd:Q5333 p:P39 ?s . ?s ps:P39 wd:Q7241336 . ?s pq:P580 ?value}