account(ex:acc1,
        http://example.org/asserter1, 

    ...
    entity(rs,[ex:created=1870])
    ...
    )


account(ex:acc2,
        http://example.org/asserter2, 

    ...
    entity(rs_m1,[ex:membership=250, ex:year=1900])
    ...
    wasComplementOf(rs_m1, ex:acc2, rs, ex:acc1)

)