PREFIX ex: <http://www.w3.org/2009/sparql/docs/tests/data-sparql11/negation#>
PREFIX dc: <http://purl.org/dc/elements/1.1/>

# The closest pre-operative physical examination
SELECT ?exam ?date { 
  ?exam a ex:PhysicalExamination; 
        dc:date ?date;
        ex:precedes ex:operation1 .
  ?op   a ex:SurgicalProcedure; dc:date ?opDT .
  FILTER NOT EXISTS {
    ?otherExam a ex:PhysicalExamination; 
               ex:follows ?exam;
               ex:precedes ex:operation1
  } 
}