@prefix : <foo:bla#>.
:a :r1 :b1.
:a :r1 :b2.
 :b2 :r2 :c2.
:a :r1 :b3.      # yes
 :b3 :r3 :c3.
   :c3 :r4 :d3.
:a :r1 :b4.      # no
 :b4 :r2 :c4.
   :c4 :r4 :d4.