query: SELECT ?sitter (SAMPLE(?item) AS ?painting)  (COUNT(?sitter) AS ?count) WHERE {
    ?item wdt:P31 wd:Q3305213 .
    ?item wdt:P136 wd:Q134307 .  
    ?item wdt:P921 ?sitter .
    ?item wdt:P180 ?sitter .
    ?sitter wdt:P31 wd:Q5 .
    MINUS { ?sitter wdt:P1299 [] }  . 
    } 
  GROUP BY ?sitter 
  HAVING (?count=1)
   
  