_:b1 . _:b1 _:b2 . _:b2 "1"^^ . _:b2 . _:b1 _:b3 . _:b3 "2"^^ . _:b3 . _:b4 . _:b4 _:b5 . _:b5 "1"^^ . _:b5 . _:b4 _:b6 . _:b6 "2"^^ . _:b6 .