PREFIX     :    <http://example/> 
PREFIX  xsd:    <http://www.w3.org/2001/XMLSchema#>
PREFIX  apf:    <java:com.hp.hpl.jena.query.pfunction.library.>
PREFIX  rdf:    <http://www.w3.org/1999/02/22-rdf-syntax-ns#>
PREFIX list:    <http://jena.hpl.hp.com/ARQ/list#>
SELECT *
{
    [] :p ?n .
    ?n apf:bnode ?label .

##    ?list list:index (?idx ?m)

##     ?x :p ?list .
##     OPTIONAL { ?list list:length ?len . }
##     OPTIONAL { ?list list:index (0 ?m1) . }
##     OPTIONAL { ?list list:index (1 ?m2) . }
##     OPTIONAL { ?list list:index (2 ?m3) . }
##     OPTIONAL { ?list list:index (?i1 "a") . }
##     OPTIONAL { ?list list:index (?i2 "b") . }
##     OPTIONAL { ?list list:index (?i3 "c") . }
##     OPTIONAL { ?list list:index (?i4 "d") . }
##     OPTIONAL { ?list list:index (1 "b") . }
}