# bindings with two variables and two sets of values

PREFIX : <http://example.org/> 
PREFIX foaf: <http://xmlns.com/foaf/0.1/> 
SELECT ?s ?o1 ?o2
{
  ?s ?p1 ?o1 
  OPTIONAL { SERVICE <http://example.org/sparql> {?s foaf:knows ?o2 }}
} BINDINGS ?o2 {
 (:b)
}