Let \Gamma be a distance-regular graph of diameter d. It is said to have classical parameters (d, b, \alpha, \beta) when its intersection array \{b_0,b_1,\dots,b_{d-1};c_1,c_2,\dots,c_d\} satisfies b_i = ([d] - [i])(\beta - \alpha [i]) and c_{i+1} = [i+1] (1 + \alpha [i]) (0 \le 1 \le d-1), where [j] := 1+b+\cdots+b^{j-1} is the b-analogue of j.
One can say that a distance-regular graph...