PREFIX arg: <http://purl.obolibrary.org/obo/> 
PREFIX foaf: <http://xmlns.com/foaf/0.1/> 
PREFIX v:   <http://www.w3.org/2006/vcard/ns#> 
PREFIX vivo: <http://vivoweb.org/ontology/core#> 

CONSTRUCT {
    ?s arg:ARG_2000028 _:vcard .
    _:vcard arg:ARG_2000029 ?s .
    _:vcard a v:Individual .
} WHERE {
    ?s foaf:firstName ?firstName 
    FILTER NOT EXISTS {  
      ?s arg:ARG_2000028 ?vcard
    }   
}