Project(
        Filter(
               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) ])
)
