Project(
        LeftJoin(
                 BGP(
                     triple(variable(s), uri<http://example.org#p1>, variable(v1))
                 ) ,
                 BGP(
                     triple(variable(s), uri<http://example.org#p2>, variable(v2))
                 ) ,
                 expr(op lt(expr(variable(v1)), expr(integer(3))))
        ) ,
        Variables([ variable(s), variable(v1), variable(v2) ])
)
