neigh(G, n) is the neighbourhood of the node n in the graph G.
neigh(G, n) = arcsOut(G, n) ∪ arcsIn(G, n).
5.3.2 has:
For a node n of the graph G, we define neigh(n) as the set of triples adjacent to n in the graph; these are the triples that have n either as subject or as object.
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5.3.2 has: