PREFIX  dc:   <http://purl.org/dc/elements/1.1/>
PREFIX  cal:  <http://www.example.org/Calendar#>
PREFIX  rdf:  <http://www.w3.org/1999/02/22-rdf-syntax-ns#>
PREFIX : <.>

SELECT ?title1 ?eTime1 ?title2
FROM NAMED <personA.ttl>
FROM NAMED <personB.ttl>

WHERE {

  GRAPH :personA.ttl {
    ?e1 cal:date ?date1.
    ?e1 dc:title ?title1.
    ?date1 cal:endTime ?eTime1.
  }.

  optional {
    GRAPH :personB.ttl {
      ?event2 cal:date ?date2 .
      ?event2 dc:title ?title2 .
      ?date2 cal:startDay ?start2 .
      ?date2 cal:startTime ?sTime2 .
      ?date2 cal:endDay ?end2 .
      ?date2 cal:endTime ?eTime2 .
    }.

    FILTER(?sTime2 < ?eTime1) .
    FILTER(?eTime2 > ?eTime1) .
  }.

}