PREFIX :      <http://example/>

<< << :s :p :o2 >> :q2 :z2 >>
        :graph  :g .

<< _:b0 :r :o4 >>  :graph  :g1 .

<< _:b0 :r :o3 >>  :graph  :g1 .

<< << :s :p :o1 >> :q1 :z1 >>
        :graph  :g .

<< << _:b0 :r :o3 >> :pb "abc" >>
        :graph  :g2 .