Intersection array
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In the mathematical field of graph theory, given a distance-regular graph G of diameter d, by definition there are integers bi and ci such that given any two vertices x and y in G at distance i, y has bi neighbours at distace i + 1 from x and ci neighbours at distance i − 1 from x. The sequence {b0, ..., bd−1;c1, ..., cd} is called the intersection array of G.