prefix foaf: <http://xmlns.com/foaf/0.1/> 
prefix time: <http://www.w3.org/2006/time#> 
prefix xsd:  <http://www.w3.org/2001/XMLSchema#>
prefix ex: <http://example.org/ex#> 
prefix thing: <http://example.org/thing#> 

select ?name where {
  ?g time:start ?start .
  ?g time:end ?end .
  filter (xsd:integer(?start) <= 1891 && xsd:integer(?end) >= 1891) .
  
  graph ?g {
    thing:maria foaf:name ?name .
  }
}