||Methods of moving attn in a node||next->|
moves attention from one arrow to the next within the set of arrows of
the same predicate. Gress fails when there are no more arrows in
that predicate, and moves to the first arrow of the predicate.
moves attention from one predicate to the next within the set of predicates
within the same node. sym fails when there are no more predicates,
and moves to the first arrow of the first predicate of the node.