 A pointed graph is a triple  (G,→, g)   such that  →  is  a relation on G  and g ∈  G.    A bisimulation  between pointed graphs  (G,→, g)  and    (H,⇒, h)   is a bisimulation  R  between  (G,→)  and   (H,⇒)   such that g   R   h.   