// Does not consider if the property slot is a variable.
if ( ! quadBlock.contains(null, null, rdfType, null) )
return quadBlock ;
quadBlock = new QuadBlock(quadBlock) ;
int i = 0 ;
// Better/clearer : do as copy over from one block to another.
while ( ( i = quadBlock.findFirst(i, null, null, rdfType, null) ) != -1 )